Add code generators for different languages

[ruflin]

To make producing of ECS data easier, ECS should have generated code snippets for different languages available. These code snippets define the ECS fields as types / objects / * in programming languages. Users using these libraries can use Auto-Complete to use the fields and can also see description of each field.

A first implementation for Golang can be found here: #249

[jamiehynds]

Closing as not something we have seen demand for or plan on implementing in the short-term.