[Erlang] Enhancements to Erlang server generator

Description

• Write specs for static exported fuctions
• Write specs for generated exported fuctions
• Add datetime/date validation
• Separate gigantic api to submodules and refactor the routing
• Add tests for the validators
• Add integrational test for the whole cycle
• Add validations of definitions with inheritance
• Add proper response validation (this list hack is so weird)
• Fix enum validation. It doesn't work correctly when the parans is in qs/header

Swagger-codegen version

Latest master (Sep 2016)

If anyone wants to work on any of these tasks for erlang-server, please reply to let us know.

Ref: https://github.com/swagger-api/swagger-codegen/pull/3758

cc @galaxie