gitconfig: Add 'dwc' alias to 'diff --color-words'.
pentadactyl: Add duckduckgo, visual bell, and a qmarks mapping.
vim: Add some more features.

This adds:
- :w!! to sudo write
- :t   for tabedit
- a markdown filetype autocmd that expands tabs
shell/rc: Change 'source' to '.', add zsh auto rehash.

'.' is compatible with bourne shell.
shell/aliases: Add 'cp' to 'cp -i' alias.