.vimrc code folding, mklinks whitelist

The major changes happened in .vimrc - added some excellent code
folding.

Changed mklinks.sh to use a whitelist of dotfiles instead of a
blacklist.

vimrc's statusline now only shows basename of files in buffer
instead of full path to files in other buffers.

A few other small changes.
Fix c-h conflict in vimrc, add `git down`

`down` alias added to .gitconfig but haven't fully tested it yet.
Merge branch 'master' into dev