Squashed 'vim-golang/' content from commit b63f8e8

git-subtree-dir: vim-golang
git-subtree-split: b63f8e84af8d5f9c29609da8c82b3628b86d5164
Merge commit '01ca1848919dd37c116805ee98a950eecb0f69b2' as 'vim-golang'
Add Go support.