Find a suitable replacement for docopt

[gabrieldemarmiesse]

Currently we use docopt to get the command line options. But this has several issues:

• Docopt is parsing a help string to understand the command line. But this help string is generated by sacred. Hence we are parsing something autogenerated by ourselves. It's redondant, error prone, not readable and not easy to debug.
• Docopt has a bug concerning the parsing, see #634
• The developement of docopt has stopped one year ago.

What is nice is that docopt isn't used a lot in this project, so it's some work to replace it but nothing unreachable. Help welcome.

[Qwlouse]

Yeah I agree. Ideally I would like to decouple the commandline interface even further, so that we could easily use different frameworks. Because sometimes people have an existing commandline system in place, and it would be great if it was easy to integrate sacred in this case. But apart from this refactoring, it seems like click is pretty powerful, popular and actively maintained.