Support for multiple input folders.  When multiple entries are provided for "-i" in options, all provided folders will be parsed in the order provided.

This functionality is useful when re-using definitions across multiple web API docs.  The common definitions can be parsed first and then the API specifics provided in a 2nd folder.
Ex:
apidoc -i example/ -i example2/ -o doc/
Merge pull request #53 from Limech/master

Support for multiple input folders.