New feature: get_single_function() for IDA Pro

[gluesmith2021]

Added get_single_function(): allows to retrieve blocks and instructions from a single function instead of the whole binary.

Two existing functions (get_functions() and get_all()) were split so that the new get_single_function() can reuse the same code.

Version was bumped to 0.2.0 so that other software may request it to use the added functionality.

[gluesmith2021]

I was not able to re-create poetry.lock, and all github check fail. It would require bumping Python verison to ^3.9 instead of ^3.8. I don't know what this implies for other projects using jvd. Nevertheless, simply bumping jvd version to 0.2.0 does not change anything to current dependencies but still fails github checks.