More snippets for go-mode. Removed some verbosity in text of old snippets.

Just added some useful snippets for Go. Also changed argument names in old snippets for clarity.
From what I can see a more correct indentation would be

    # -*- mode: snippet -*-
    # name: switch
    # key: switch
    # --
    switch $1 {
    case $2:
         $0
    }


which however for some reason still does not work properly (maybe go-mode changing things not sure).

But I'm open to be convinced otherwise..