Idea: Make get_files accept a glob

[jplatte]

So instead of giving it a directory name, you'd say dirname/* or dirname/*.html. And you could also do dirname/*/*.html (all html files in direct subdirs of dirname), or dirname/**/*.html (all html files in dirname and any subdirs of dirname, no matter how deep).

I think this is gonna be a lot nicer than what's there now, and readdir-style functionality can be provided as a separate function.