Adding ign router

[LBasara]

I've recently grown fond of the geoservices provided by the French IGN, which include routing and isochrones/isodistances, see here.

I'm thinking about adding it to routingpy, but the service being targeted towards a French audience, with french-only documentation and (as far as I can tell) working only for French territory, ask about the relevance to avoid frustration on both sides.

Thanks :)

[mthh]

Adding the IGN router seems like a good idea to me.
In addition to offering OSRM and Valhalla, it offers a method based on BD TOPO / pgrouting, which I find interesting for comparison purposes for a French audience.

So I'm totally up for reviewing/accepting a PR adding it!

[mthh]

Closed by #157.