weppy 1.3 (codename Nunki)

Changes since 1.2:

• Minor bugfixes
• Added proper support for 'big' id and reference fields to ORM
• Added url_prefix global routing paramater to App
• Allow to specify different templates_encoding for templates loading in
  application config
• Added migrations_folder variable to database configuration to support
  migrations with multiple databases
• Added support for Python 3.7
• Refactored join and including options handling in ORM
• Added cast method to ORM Field
• Added cast options to has_many decorator
• Optimized pipeline flow
• Optimized router match code