Added two themes

- Raven (for Dark colorschemes)
- Silver (for Light colorschemes)
README: fix link to powerline font install docs
Added theme support for console vim

- Both themes (raven and silver) have been updated
Merge pull request #613 from meonkeys/patch-1

README: fix link to powerline font install docs
Merge pull request #582 from Pychimp/two-themes

Added two themes
Update raven.vim

- Fixed the incorrect cterm background value for airline_warning
Merge pull request #614 from Pychimp/two-themes

Update raven.vim