Vim: Y to yank entire line

Closes #597
Close enough implementation of :x.
Vim numbers: Implement C-a C-x
Vim numbers: Add tests
Explicit export list in Yi.Buffer.Indent.
First try at achieving magical block autoindent in vim keymap.
Provide autoindenting variant of bdeleteB.
Update module comment for Yi.Buffer.Adjusted.
Remove garbage.
Make test3CharB get characters
Almost decouple layouting and drawing in vty frontend.

Also fix jumping modeline.
Merge pull request #594 from siddhanathan/pull

Vim: Implement C-a and C-x
Extract some layout code from Yi.UI.Vty into Yi.UI.SimpleLayout.
Try --force-reinstalls in attempt to fix travis build.
Remove some unneeded code.
Respect file permissions, if readonly

Fixes issue #145
Use unless
Add deleteRegionWithStyleB in Yi.Buffer.Adjusted.
Vim: Revert behavior of Y

Reverts commit 22c924a
Label main vty thread.