general PEP8 clean-up (actually a test commit)
change .gitignore section (test commit)
update vodml schema to the latest version

Also had to update the xml test instances
and some python code that was broken by the schema
update.
Update README.md
PEP 8 clean-up (test commit)
refactor the model module

unstable code
tests are broken
drop model-extends-package from vodml schema

fix sample models and code accordingly
also, fix some code for enumeration
add resolvers and some code generation logic
big refactoring and simplification

dropped most of the metaclasses
added usage of descriptors
add AttributeLists and tests, plus some cleaning
Merge pull request #1 from olaurino/develop

Develop