Solve Issue 2233: Routing instructions disappearing too early in roundabouts.

Hi Victor:

I did a solution for this problem. Idea is to also know end point for roundabouts. So we can avoid changing to next direction until roundabout end is reached and visual direction remains visible. 
Distance has a behaviour that could be surprising for users, but is what I can do without changing a lot of code. Firstly drops as we arrive to start of roundabout (like previously) and when entering roundabout grow up to roundabout distance and goes to 0 when we arrive to marked exit.

There are 2 commits. one with the solution and another with minor simplifications i found.
I trush you will found this interesting.

Regards, Javier.
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