Recover and adjust for `macOS` (#137)

*   Use `mkdir -p` instead of unsupported `--parents` on `macOS`.
*   Spec: `FS_28_84_41_40.multi_level_bootstrap.md`.
*   Spec: `FS_69_15_45_21.template_instantiator.md`.
*   Fix: use `load_tags_last_days: 360` to let integration test see futher back into history.
*   Set dependency version constraint: `marshmallow<4.0.0`.

Initial split of packages (#131)

Start splitting single `argrelay` package into multiple one.

Package:
*   Add initial setup for `import-linter`.
*   Refactor into `argrelay_api_server_cli.schema_request.*`.
*   Refactor into `argrelay_api_server_cli.schema_response.*`.
*   Refactor into `argrelay_api_server_cli.server_spec.*`.
*   Add explicit `argrelay_data` and `argrelay_docs` package dirs.
*   Roll the earliest supported Python version to 3.9.

Docs:
*   Write `the_problem_argrelay_solves.md`.
*   Update `TODO_78_94_31_68.split_argrelay_into_multiple_packages.md`.
*   Spec `TODO_23_17_31_04.publish_index_model_by_delegators.md`.
*   Spec `TODO_01_47_82_92.keep_applying_best_practices.md`.
*   Spec `TODO_91_90_42_61.complete_parsing_and_interpretation_tests.md`.
*   Spec `FS_84_11_73_28.supported_python_versions.md`.

GUI:
*   Prevent scroll on input focus.
*   GUI add bottom blank area to prevent elements from jumping.
*   Add GitHub ribbon.

Major: split delegators to support only a single func (#127)

*   Insert `AbstractSingleFuncDelegator` into the hierarchy to serve those which implement only one func.
*   Split all other delegators each implementing only one func.
*   Rename delegators to use common prefix of inheritance: `AbstractDelegator` -> `DelegatorAbstract`.
*   Implement `DelegatorSshDst` to provide simple working example of wrapping `ssh` command for demo.
*   Add post validation for data loaded by `DelegatorDataBackendSet`.
*   Update docs:
    *   Add readme section "How to use it?".
    *   Move readme multiple sections to `project_origin.md`.
    *   Move readme section "Beyond the demo" into `project_walkthrough.md`.
*   Fix empty prop value validation.
*   Fix `normalize_tree` to handle the case with multiple nested `surrogate_node_id_`-s.

Implement `func_id_set_data_envelopes` (#123)

*   Be able to update server data via `func_id_set_data_envelopes`.
*   Send client `stdin_data` on `CompType.InvokeAction` to store it via `func_id_set_data_envelopes`.
*   Include `CallContext` into `InvocationInput`.
*   Keep separate caches per collection.
*   Invalidate cache per collection on `func_id_set_data_envelopes`.
*   Mock `stdin` by `EnvMockBuilder` for testing.
*   Rename: `ClassCollectionMeta` -> `ClassCollection`.
*   Spec `TODO_65_62_32_33.extend_data_manipulation_API_by_del_and_invalidate.md`.

Remove `static_data` and make loaders populate `envelope_collection`-s (

#121)

*   Stop using `static_data` from `server_config` to communicate loaded data.
*   Streamline loading of `envelope_collection`-s by loaders.
*   Get through func loading process:
    *   `index_prop`-s for func `data_model`
    *   func `data_envelope`-s
*   Allow disabling loading Git repo entries by `GitRepoLoader`.
*   Run Python `check_env` in `dry_run` mode first.
*   Configure `envelope_class_to_collection_name_map` for `ConfigOnlyLoader`.
  *   Take explicit `collection_name` by `populate_search_control`.
*   `@/conf/argrelay_server.yaml` schema changes:
    *   Remove `class_to_collection_map`.
    *   Remove `index_props` from `envelope_collection`.
*   `@/conf/argrelay_plugin.yaml` schema changes:
    *   Put plugins into `server_plugin_instance_groups`.
    *   Rename `plugin_instance_entries` -> `server_plugin_instances`
    *   Remove `reusable_config_data`.
*   `@/conf/check_env_plugin.conf.yaml` schema changes:
    *   Rename `check_env_plugin_instance_entries` -> `check_env_plugin_instances`
*   Remove permutation by `use_single_collection` in `test_QueryEngine_perf.py`.

Improve `data_model` validation (#120)

*   Validate both ways: `search_props` <-> `index_props`.
*   Relax validation where possible (report stats instead).
*   Configure generic `GitRepoLoader` with `class_name`-s it is supposed to load.
*   Fine-tune search_props for `Git*` `data_envelope`-s.
*   Rename `MetadataDelegator` to `DataBackendDelegator`.
*   Move logging and tracking calls under `ProgressTracker`.
*   Report `report_collection_sizes`.
*   Spec `TODO_98_35_14_72.exclude_class_name_from_search_control.md`.

Make loaders `list_data_models()` (#119)

*   Define `data_model`-s by loaders.
*   Update GUI spinner to retain state between requests.
*   Optimize validation on server start (avoid scanning all `data_envelope` twice):
    *   Validate `index_prop`-s for all `data_envelope`.
    *   Validate that all `search_prop`-s are listed as `index_prop`-s. 
*   Spec `FS_45_08_22_15.data_model_manipulation.md`.
*   Spec `TODO_89_50_17_63.fine_tune_list_of_index_props.md`.
*   Define `ReservedEnvelopeClass.ClassNoData`.
*   Rename `LoadProgressState` to `ProgressTracker`.

Use explicit `import encodings.idna` ahead of fork (#118)


*   Revert attempt to fix TODO_30_69_19_14 client spinner hangs by using `urllib3` instead of `requests`.
*   Try explicit `import encodings.idna` ahead of fork instead.

Use `check_env` for GNU Readline settings + update the docs (#117)

*   Implement `check_env` verification for GNU Readline settings:
    *   `show-all-if-ambiguous`
    *   `show-all-if-unmodified`
    *   `skip-completed-text`
*   Prefix all existing `TODO_` with `TODO: ` to syntax highlight them.
*   Force convenient GNU Readline settings in `@/exe/dev_shell.bash`.
*   Implement animated spinner for GUI.
*   Make `echo_command_on_stderr` true by default for `ConfigOnlyDelegator`.
*   Spec: `TODO_96_01_13_29.multiple_bootstrap_stages_to_instantiate_configs.md`.

Reduce plugin instances by reuse (#115)

*   Remove all `FuncTreeInterpFactory.*` except `*.default` and `*.check_env`.
*   Do not mark GUI status as failed on abort due to invalidated input.
*   Spec `TODO_06_54_83_58.extend_via_func_instead_of_delegator.md`.
*   Switch to min Python version = 3.8.