usatxl: Texas State Highway Loops

[yakra]

This system is almost ready to activate.
Prior discussion on AARoads
AFAIK, there are no outstanding issues in need of attention.
Seeking public comment & peer review.

[yakra]

This system is pretty much ready to go live. I'm confident that NE2's review on AARoads was a very thorough one. That said, it's still not undergone any systematic review from a CHM/TM veteran to get "standards" stuff such as waypoint labels, placement, etc.
Does it need one? It's my work, so of course I think it's fine!
If I don't hear anything by the end of May, I'll put in a pull request to activate.

[yakra]

https://github.com/TravelMapping/HighwayData/pull/606