Extract the converters registry/engine into an independent project

[smarie]

The API for converters, as well as the notion of converters registry and the engine able to create chains of converters, could be useful to anyone (outside parsyfiles). Therefore it would be good to create an independent project from this.

Next step in that project would be to replace the expert-rules-based conversion chain generation by a graph-based algorithm relying on one of the following:

• http://networkx.github.io/
• http://igraph.org/
• https://graph-tool.skewed.de/
• https://github.com/pmatiello/python-graph
• https://github.com/erocarrera/pydot
• https://github.com/erwinvaneijk/bgl-python
• https://www.python.org/doc/essays/graphs/
• http://www.python-course.eu/graphs_python.php