Change how b:undo_* variables are set

This simplifies these files and reduces the line count a bit. This
commit also fixes a few minor, latent bugs in the ftplugin and indent
files.

Remove extraneous header comments from vim files

Manage dotfiles directly in home directory

Add autoformat plugin and touch up some ftplugins

Remove 'if &filetype' guards from ftplugins -- at worst they prevent
ftplugin "chaining" (e.g. the liquid ftplugin sources the html ftplugin)
and at best they.... don't really do anything.

[vim] Create yaml ftplugin