A few more changes for Vim

Tweak the text editing settings (softtabstop, textwidth, etc).

Add some settings to turn on folding and colorcolumn.

Add the undo_ftplugin changes that my previous patch forgot.
Why would you do this? It should just be omitted.  (The docs should be clarified about what it *actually* does also, because if I have formerly done `set foldlevel=99`, for example, `2` will be functionally equivalent to `1`.)