Support arbitrary middleware

Was playing around with budo-less and had the idea that budo could support any arbitrary middleware that followed a particular pattern (maybe like simple-less-middlewares), and would map that to a cli switch when budo is invoked.

I imagine budo doesn't want to get bogged down with heavy, convoluted configuration (see: webpack compared to browserify itself), but I could also see a usecase for two to three middlewares being all that's necessary to have a full-fledged dev server running within minutes without a ton of task runner or watcher configuration (see: gulp), etc.