MapsAPIGenericEngine uses HttpClient incorrectly

[stephajn]

The MapsApiGenericEngine creates a new HttpClient for every request it makes. As a result, under load, this library would burn up all of the available sockets on a machine because it is not reusing the same HttpClient instance.

This class should be updated so that the HttpClient is created once as a static instance instead.

[maximn]

Right, I believe it used to work differently in older versions.

You're welcome to suggest a pull request.