Add support for add --patch

[clobrano]

Is your feature request related to a problem? Please describe. The commit view only allows to add an entire hunk

Describe the solution you'd like Very often is useful to only add part of the hunk, via git add --patch

Describe alternatives you've considered There is no specific alternative

Additional context This is one of the most useful features implemented in fugitive

[CKolkey]

You can partially stage a hunk by using visual-line mode V to select the region to stage. Works with unstaging and discarding too.

[clobrano]

My bad, I didn't try the uppercase V