Allow all files (not just targeted files) to be included

[ebenoist]

First off, this is a fantastic project. I was able to rewrite a squirrels nest of node code with this library in much fewer lines and the API here took care of a lot of the work I was doing before. Thank you!

One snag I hit was in implementing a compiler for a number of protos from different projects that I'm currently tying together by including each directory in my import path. I can't compile each separately because my target is format that doesn't support imports at all.

Because of the decision to only include those files in the output request, I have to glob all of the protos I have, which break a number of their import resolutions instead of just pointing the compiler at the one entry point proto that imports the rest.

Specifically this decision makes globbing multi project protos difficult. Is there any consideration to making that behavior configurable?