Added sources hash key and source method to podfile
Add documentation folder as gitignore
Moving sources to contain names of repo sources instead of endpoints

Also updating previous work according to comments of pull request.
Modify aggregate to support given repositories directories
instead of default one
Update doc to specify order of sources
remove debug output
Remove aggregate repo_dirs argument
Passing array of Pathnames for aggregate tests
Fixing test "returns all the sources"

Order of repo sources does matter now.
But in this test it does not.
So for asserting we make sure we have the same order - alphabetic order
ADD comment about sources priority
Moving default Source to cocoapods gem

Removed private helper for master repo
Default sources to return empty array instead of nil