Move all parser definitions to powerline.commands.*.get_argparser()

Reasoning: they will be easier to reach there. It will also be possible to use
specific ArgumentParser class that will just collect data for sphinx.
Improve powerline-config help and require --shell argument
Make all metavars uppercased
Add `man` documentation target

Fixes #1131
Add new documents to the main TOC tree
Also add documentation for `powerline-lint`
Update powerline-release script to use live ebuild as the base

Reasoning: I am going to add man pages support to the live ebuild, but it does 
not make sense to add this to the 1.0 ebuild previously used as the base. Since 
new features will likely continue to appear in the live ebuild powerline-release 
script was modified to do the right thing under new circumstances.
Merge pull request #1134 from ZyX-I/man

Generate manual pages

Replaces #1132