Feature/loops

[mikedbjones]

Thank you for this project, it has been very useful for some GPX route comparison work I've been doing. I have added some functionality to handle loops and linear routes.

Added handling of loops:

• rotates loops so that start points match for comparison purposes
• detects whether one loop is the reversal of another. If so, reverses one of the loops for comparison
• added argument -r to negate the effects of reversal detection (to force reversal if it is not detected, or avoid reversal if it is)

Added similar reversal logic for linear routes.

See GPXs and PNGs for derwent_loops and stanage_linear for examples.