Added Forge-compatible semantic versioning classes.
Use new method to calculate dependencies in a more robust manner.
Some refactoring and improvements in models:
 * Added custom managers for natural key support, and moved `Module` classmethods to manager instance methods.
 * Use `json` instead of `simplejson`, and moved `views/json.py` to `views/utils.py` to prevent namespace clash
 * `error_response` is v1 only, so moved into v1 views
 * Use non-deprecated Django/Python APIs
Fix tests, and make existing ones specific to v1 API.
Fixed regression where ranges weren't properly parse and added tests for forge's semantic version subclasses.
Added comments/docstrings, caching, and some simplification.
Change manage.py so that it may work again.
Merge pull request #5 from jbronn/dependency-improvements

dependency improvements, fixes #4