Gemeaux

Following the Specs

* Added `TemplateResponse` & `TemplateHandler` classes for generating Gemini content using template files.
* Make sure returned responses endlines are not mixed, only CRLF.
* Handling mimetypes other than `text/gemini`. Clients would have to download them instead of trying to display them. Example app is amended.
* Redirect clients when pointing at a static subdirectory without a trailing slash. It caused misdirections because the client was requesting the "/document.gmi" instead of the "/subdir/document.gmi".
* Improve application resilience after auditing it with [gemini-diagnostic](https://github.com/michael-lazar/gemini-diagnostics). Everything is not perfect, but that's a good start, to be honest.
* Added `BadRequestResponse`, `ProxyRequestRefusedResponse` classes

Other changes

* Improved conftest for pytest using fixtures for document content.
* Return version number when using the `--version` option.
* Display version number at startup on the welcome message.
* Added mimetype of response to the access log.
* Added documentation for Handlers.

This is the first release of `Gemeaux` server.

Main features

* Implementation of the TLS-required Gemini protocol communication workflow. The most used parts of the specifications are covered, but there are still lots of improvements to make,
* Serving a static directory tree made of `.gmi` files. Configuration options: index file name, directory listing,
* Serving a textual content,
* Redirection (permanent or temporary) responses,
* Customizable Handlers,
* Tested with Python 3.6, 3.7, 3.8 through pytest and Travis-CI.
* Example application to show how to use the core features.