Do not depend on pip internal parsing of requirements.txt, reference
setup.py from requirements instead. Same for requirements_dev.txt, but
now use the extras_require and reference the 'testing' feature
dependencies.

See: https://caremad.io/posts/2013/07/setup-vs-requirement/
See: https://stackoverflow.com/a/27271396


Signed-off-by: Oldřich Jedlička <oldium.pro@gmail.com>

The builds will fail to due valid flake8 problems. Anyome is welcomed to solve some of them as I will not make a new release before they are all fixed.

Signed-off-by: Sorin Sbarnea <sorin.sbarnea@gmail.com>

Signed-off-by: Sorin Sbarnea <sorin.sbarnea@gmail.com>