Merge pull request #291 from DXist/feature/positive_integer

XMLSchema positive integer primitive
Couldn't create complex model without defined _type_info
Add mapper for Django models
Easy way to convert complex model to dict
Tests for model rpc service
Pass pattern strings instead of compiled regexes
Strip metachars, check has_default
Django uses 32 bit integers by default
Support field list to exclude from mapping
Unknown fields check
Each mapper instance has own registry