Plantweb

This fixes some issues when using Plantweb in Windows:

- 15
- 16

Bad release. No not use it. Ups.

**New**

- Added documentation on how to run a PlantUML docker container to simplify
deployment.

**Fixes**

- Fix 9 passing source files to the Sphinx directive as an absolute path.
- Fix 7 source files passed as argument to the Sphinx directive failed to
render correctly.
- Fixed test suite to be compatible with newer versions of Sphinx.
- Fixed several PEP8 violations.

**Changes**

- Improved algorithm to gather configuration for a git repository root.
- Test suite now test Python 3 with Python 3.5 instead of Python 3.4.

**Fixes**

- Fix 1 that caused diagrams rendering to fail with a 404 in Windows OSes.

**New**
- Sphinx directives now support passing a source file as argument.

**New**
- Added a set of Sphinx directives `uml`, `graph` and `diagram`.