Add coalesce/1 function to directly merge a list of schemas
.conf -> .config translation changes

- No longer require a .conf
- Merge configuration in order of .conf -> schema defaults -> config.exs
  settings.
- **Breaking Change**: Transform functions now require one of two
  signatures, mapping/val, or mapping/val/accumulator. The accumulator
is provided if you have more than one setting pointing to the same
target setting. A good example use case is lager backend handlers
(console, file, etc).
Implement list datatype
Rewrite schema writer from scratch. Much more flexible and solid now.
Update all conform tasks to use new API
Add a bunch of sample data and add/update tests
Fix bug where defaults are provided using the wrong datatype and no error is thrown.
Update README
Clean up unused variable warning
Version 0.9.0