#27 Minor documentation bug: oqt_get_video_frame_duration

[Erik Demaine]

Minor point: The documentation for
"oqt_get_video_frame_duration" is under the section
"oqt_get_video_sample_duration". Need to change
"sample" to "frame" in the documentation string. This
bug makes it hard to find the documentation for this
function, given that things are sorted alphabetically.