Fix the `gorilla/mux` import

gorilla moved to GitHub (https://github.com/gorilla)
Merge remote-tracking branch 'coffeejunk/import_mux'
initial changes to generate play buttons, ref #37
initial generation for play.golang.org linking, ref #37
missing some generated files
just panic here for now
simplify parseHashFile
switch to if
add trailing newlines
use the gopher logo
move image placement styling to css
place gopher run link in top-right of rendered go source
Merge branch 'play'
fix worker pools link
rebuild
Move `state` variable internal to stateful goroutine.
Tweak wording and remove trailing whitespace
Merge branch 'stateful-goroutines-internal-state'
Rebuild
Make the stateful gorouting a single block