Replace static compilation with package staticdir

The contents of static.go have been removed and replaced with the more
flexible package staticdir, which will be more suitable to our future
needs. This will allow us to fix @lukevers's new issue #188 much more
easily by implementing our own CopyFunc.

I had originally planned to delete static.go entirely, but I believe it
makes more sense to keep it there with CompileStatic and whatever new
CopyFunc we write.