fix annotation import

add annitations import to defer evaluation of annotations in rf

Merge pull request #145 from RemDelaporteMathurin/fix-scikit

`scikit-rf` is now really optional

fixed pid example in docs

Merge pull request #137 from milanofthe/block-sorting

handle eventful blocks separately from external events

Merge pull request #122 from milanofthe/roadmap-overhaul

the roadmap now automatically updates from the issue tracker

Merge pull request #107 from milanofthe/more-logging-info

add number of internal events to logging for adding blocks to simulation

Merge pull request #103 from milanofthe/block-lib-extension

cleanup and improvements to simulation loop and new blocks

Merge pull request #101 from milanofthe/improve-test-coverage

improve test coverage

Merge pull request #96 from milanofthe/simulation-interrupt

Simulation interrupt