Support ingesting proto dirs and specifying a proto file

[JakeWharton]

Lots of times you are decoding your own protos and it would be nice if you could point at a proto dir and FQN of a proto.

For example,

$ protogram --protos ../protos example.User 0a827fbc073edda07

[mattprecious]

Could also do this on the web in theory.

[mattprecious]

Maybe not. You'd have to pass the entire contents of the proto files through as an argument.

[JakeWharton]

There's a new API coming that will provide access to a folder

[JakeWharton]

Web version blocked on availability of https://caniuse.com/#feat=native-filesystem-api