Add some debug logging

Log the files being read and the merges being performed when Composer is
run in verbose mode.
Change configuration format

The configuration format specified in the README file and the code/tests
differed. The new format is a slight variation on the README format and
should be easier to extend if we add more configuration settings in the
future.
Merge pull request #5 from bd808/issue/2

 Change configuration format and add verbose logging