feature request: include distance_from_start in NearestLocationsData class

[pleasantone]

I've added a a change to the code in my own private repo that includes the distance_from_start returned from get_points_data() into the named tuple returned by the get_nearest_location and get_nearest_locations routines.

I'm not going to bombard you with a pull request before asking if this change would even be welcome?

My hesitancy in submitting is that it does add an additional element to the NearestLocationsData class, so if someone is accessing it as a tuple, for example, in a for loop, it could cause issues and break the API. However, I doubt many people do, since it is a named tuple, but it is possible.

Why is this useful?

It's carries over expensive to calculate data from get_points_data(), and it's really wonderful to have if you're matching waypoints to tracks for printing out data about a route. https://github.com/pleasantone/gpxtr uses it (had to extend the GPXTrack class since monkey patching wasn't working for me) to produce nice little tables about a given multi-day route:

day1 210 miles: Sunrise: 07:20, Starts: 08:00, Ends: 14:59, Sunset: 16:56

Lat,Lon	Name	Dist.	G	ETA	Notes
37.2563,-121.7922	11 SilverCreek	0		08:00	Circle, Green
36.7905,-121.3219	12 Tres Pinos	54/54	G	09:49	Gas Station (+0:15)
36.1369,-120.3626	13 Coalinga	90/144	G	12:49	Gas Station (+0:15)
36.3267,-119.3442	14 Visalia	65/209		14:59	Lodging

day2 208 miles: Sunrise: 07:08, Starts: 08:00, Ends: 14:54, Sunset: 16:49

Lat,Lon	Name	Dist.	G	ETA	Notes
36.3267,-119.3442	14 Visalia	0		08:00	Lodging
36.6830,-119.0225	21 CA245	44		09:28	Waypoint
36.7545,-119.1720	22 Clingans	57/57	G	09:55	Gas Station (+0:15)
37.1070,-119.3189	23 Shaver Lake	57/115	G	11:49	Gas Station (+0:15)
37.2356,-119.2340	24 Huntington	126		12:13	Waypoint
37.2356,-119.2340	24 Huntington	131		12:22	Waypoint
37.1070,-119.3189	23 Shaver Lake	41/156	G	13:12	Gas Station (+0:15)
37.3397,-119.6442	25 Oakhurst	51/207		14:54	Lodging

day3 167 miles: Sunrise: 07:12, Starts: 08:00, Ends: 13:35, Sunset: 16:48

Lat,Lon	Name	Dist.	G	ETA	Notes
37.3397,-119.6442	25 Oakhurst	0		08:00	Lodging
37.5512,-119.9235	31 Midpines	30		08:59	Waypoint
37.7107,-120.1971	32 Coulterville	66		10:13	Waypoint
37.6848,-120.3306	33 La Grange	77/77	G	10:34	Gas Station (+0:15)
37.7121,-121.7237	34 Livermore	90/167	G	13:35	Gas Station (+0:15)

Some of the changes I needed to make were supporting the idea that "a track might be part of a multi-stop(day) ride" and I needed to have a track-specific version of get_nearest_locations(), and the idea that if a path crosses itself (see day 2), the waypoints should show up multiple times, hence not being able to use get_nearest_location().

The milage was pulled off of my extended version of NearestLocationData returned by get_nearest_locations().

[pleasantone]

I'm happy to submit a pull request if the concept of adding another field to the tuple is acceptable.