Swagger-to

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* made py-client more robust to parameter names (e.g., those with non-letter prefix or suffix such as _fields)

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* fixed a bug when generating python code for a request which does not provide any parameters.
From now on, authentication is provided in such requests.

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* swagger-style exempts descriptions of responses to start with a verb. This is necessary since certain clients produce
illegible descriptions in their code (*e.g.*, Python client).

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* swagger-to-go-server and py-client support header parameters.
* swagger-to-go-server and py-client resolve parameter name conflicts by prefixing.
* swagger-to-py-client stringifies primitive parameters with ``json.dumps`` when passing them
in headers, queries and form data.
* Endpoint paths are escaped in documentation generated by swagger-to-elm-client.

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* Added new line before ``:return:`` in swagger-to-py-client.
* swagger-to-py-client capitalizes the first letter of class and request function docstrings, respectively.
* Stripped trailing white spaces in swagger-to-go-server and py-client templates.
* Added ``date-time`` test case for swagger-to-go-server and py-client.
* Fixed contract violation in go server due to one-line imports ending in a superfluous new line.

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The major change is:

* Made all functions protected in the modules responsible for code generation.

This impacts only the users which used swagger-to as a library. This change does not affect users which use
swagger-to only as CLI.

The minor changes are:

* Rewritten go-server and py-client generation with jinja2 template engine.

The generated code is semantically equal to the previous version, but a bit more readable and easier to diff
since we enforce now the line width of 100 columns and split argument lists into multiple lines.
* swagger-to-py-client includes a response description in the docstring of the request function.
* Refactored tests into a hierarchy of test case directories
* Added test cases with files, empty objects and objects with optional fields to swagger-to-py-client and go-server.