Signed-off-by: Muhammad Falak R Wani <[email protected]>

blame: fix typo s/Widnows/Windows/

Fix readme: libgit2 version

std::path::Path is imported for use towards the bottom of the example. No point in using a fully qualified path

* Add support for custom git extensions

This would allow one to use git worktrees together with sparse-checkout.

Reference: libgit2/libgit2#6031

* Mark extension methods unsafe

* Replace custom spin-lock in tests with serial-test crate

* Rewrite tests as integration tests

Co-authored-by: Simon Gasse <[email protected]>

The git glossary mentions both verions. However in-code, only the first
variant is used. This commit harmonizes the usages:
https://git-scm.com/docs/gitglossary#Documentation/
gitglossary.txt-aiddefcommit-ishacommit-ishalsocommittish

Co-authored-by: Simon Gasse <[email protected]>

When someone vendored `libgit2-sys` he may exclude `.git` folder.

When such things happened an attempt to build it may lead to error like: `fatal: not a git repository (or any of the parent directories): .git`.

The only way to fix it is using system's `libgit2` which may lead to `invalid version 0 on git_proxy_options; class=Invalid (3)` at some cases.

* Bump libgit2 to 1.4.0

* Libgit2 1.4.0 fixes