Add dummy class for dumping to GPX
Add very simple GPX export

It needs to output meaningful extensions. The output at this point
is readable as a track though.
Add schema test for GPXData

It has some extensions to GPX that are readable by Strava.
Add byebug for debugging
Add GPX serialization for cadence

Uses Cluetrust GPX extension
Do not include element if not present
Add dist extension support

PWX may not always include it.
Add heart rate extension support
Add temperature extension support
Add power extension support
Generate time elements from time offsets

If the time element is not present in the PWX, then calc it and
add it to the parsed PWX document.
Add simple conversion script
Move extensions into namespace for gpxdata
Add author name to GPX export
Add author link to GPX export
Classify the GPX track with the PWX sport type
Add basic lap data to GPX Export
Add option parsing to conversion executable
Use more specific xpath in specs
Extract parts of serializer to methods

Trying to avoid one large method for serialization.