Bpc-walrus

* minor bugfix in function (with return type annotations) processing

* fix argparse help format string bug (many thanks to gousaiyang)

Get all errors from parso, as hints from davidhalter/parso89

* updated bash completion
* updated README
* fixed lambda conversion
* fixed line seperator guessing
* added universal unique UUID 4 generator
* added some more test cases (need reporting issues to `parso`)

* fixed classvar conversion error
* revised linting system
* revised packaging
* revised unittest

* implemented conversion algorithm to convert `:=` (walrus) operations / **assignment expressions** to pre-3.8 compatible codes
* implemented auto detection of line seperator and tab size based on source code context