ENH: moved models into subdirectory
ENH: updated examples and solutions to import models from quantecon.models
DOC: updated docs to automatically infer models/tools

No more static lists! All automatic!
Merge pull request #38 from jstac/model-subpackage

Model subpackage
Modified discrete_rv to use decorator notation for properties
Added changes from distributions branch
MERGE: merged in subpackage and distributions changes