FieldHint combines arbitrary fields from the input clip, and optionally adds Telecide-compatible postprocessing hints.

usage:
FieldHint(clip, string ovr, bool show)

ovr: required.
Filename from which to read field pairs.
Format:
	0,0,-
	3,42,+
	1,2
Each line consist of a pair of numbers: the frames from which to take
the top and bottom fields, respectively.
The optional 3rd parameter sets postprocessing hints.
("+" => mark as interlaced. "-" => mark as progressive.)

show: (default: false)
Prints the field numbers and overrides on each frame.
