Add behaviour section, slightly reorganise
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Move conditional loading of Sunset from gvimrc to vimrc

Seems Sunset will have loaded before $MYGVIMRC is sourced.
Improve command-line completion
Set a default textwidth, make colorcolumn dependent on it
Remove unnecessary else condition
Remove need for foldmethod=marker modeline in Vim scripts
Add Gundo mapping
Add various improvements from Steve Losh's vimrc

For details:
https://bitbucket.org/sjl/dotfiles/src/021398e3fd15394e194f62ae3e0c68555bb7da18/vim/vimrc?at=default
Add header