Add go vim plugin

Adds syntax highlighting and other filetype plugins for go. This
package is a mirror of the official repo's vim plugins.
README: add new plugins

Add:
* surround.vim
* golang
unimpaired_paste: add `yi` mapping

I often find that I want to delete the line inserted from the `yo`
mapping. This adds a mapping that doesn't add the line in the first
place so I don't have to go back and delete it after pasting.