files cache

[jonschlinkert]

Resolving generators is already fast, but to make it as close to O(N) as possible we can implement a files cache that reads in a glob of files, then all generator matching would happen against the returned array.

This way we're only hitting the file system once - or at least limiting the number of times we directly hit the fs in generate. users can do whatever they want in their generators.

the files cache would be exposed to the instance