supply **kwargs to all methods of all routers

[nilsnolde]

in #41 (comment) we realized that the **kwargs are not even used when they're passed to a method. instead of removing that parameter, we should make use of it and simply append the whole thing to the request parameters. reason is that we likely won't keep up here with all the changes of the individual router arguments to APIs which will be added in the future and this provides a means of passing those anyways, sort of a safety net for our (and the community's!!!) laziness;)

[nurikk]

This is exactly what I need! I've created PR adding kwargs support for osrm #49

[nurikk]

Please help to review
#59