However, I kept information on how to achieve the same thing with
`custom_environment()` in the test.

Related to #234

Unfortunately, installation of a executable script has proven to be so
difficult thanks setuptools gloriousness, which will force me to remove
that feature

Helps fixing #35

Also, the production status was changed to 'stable', which should
have been done much earlier.

This should help getting the latest version

All performance tests still print to stderr, but do so in a py3 compatible way

There is more work to do though, as many imports are still incorrect.
Also, there are still print statements

E201 whitespace after '('
E202 whitespace before ')'
E203 whitespace before ':'
E225 missing whitespace around operator
E226 missing whitespace around arithmetic operator
E227 missing whitespace around bitwise or shift operator
E228 missing whitespace around modulo operator
E231 missing whitespace after ','
E241 multiple spaces after ','
E251 unexpected spaces around keyword / parameter equals