Added recursive option

Now you can organize your yaml files into subdirectories and apply them
all just passing --recursive option or adding the proper configuration
file option.

In adding support for multiple paths the Builder.load_files method was
reworked to be backward compatible with individual paths or file-like
objects, while also now handling being passed a list of paths or
file-like objects to be parsed.

Change-Id: I126751e347622716c592c6ed1a57b8acb7bf79a4
Merge "Added recursive option"