add elevation to exif tag as well, unless it doesn't exist in the GPX
Merge pull request #18 from mprins/interpolate_image_direction

Add a script to interpolate direction based on GPS EXIF tags prior to upload
Merge pull request #19 from mprins/altitude_to_exif

add elevation to EXIF tag as well, unless it doesn't exist in the GPX
add an option to provide an offset camera angle, eg for a side looking camara. angle should be positive for a clockwise offset.