Make GstClockTimeDiff a new type
The following discussion from !600 should be addressed:
There's not much API using
ClockTimeDiffbut if you think that makes sense, go for it :)
IMHO we should use it more often in C. Even something like
GST_BUFFER_DURATION()is technically a
GstClockTimeis an absolute point in time while
GstClockTimeDiffis a duration.