additions to andrewhao-gpx

Hi,

I've made some changes that might be of use:

Made the unit tests work under ruby 2 (probably breaks 1.8.* though)
Made it deal *slightly* better with gpx extensions and namespaces.
Added funcitonality to smooth gpx tracks (using fairly basic averaging algorithm)
Added executables to bin/ to print the distance of a gpx file and to smooth a gpx file

Let me know if this is useful,

Keith