Diverse fixes

[flying-sheep]

• python 3
• can be imported (that needs a .py) extension
• argument parsing and error output doesn’t happen at import time but when executing.

check out https://github.com/nygenome/taxmaps/pull/1/files?w=1 for non-whitespace changes

[brwnj]

The lack of merging such basic functionality like Python 3 support would lead me to believe these codes are already dead. And this pull request was made almost a year ago.