add docs for get_distance()
add rounding distance to handle gpx methods
add handle gpx method: get_segment_start_and_finish_times()
add handle gpx method: get_segment_dist_and_ele()
 #84: add new gpx file for tests
 #84: add tests for gpx handler
 #84: add helpers: km2mi and mi2km
 #84: add tests for computing best times for route
 #84: add methods for computing best times for route