vdecimate: Replace tabs with 4 spaces
vdecimate: Add support for override files

Supports specifying drop frames:
   12345 -
and decimation patterns:
   12345,54133 +++-+

vdecimate doesn't care about hybrid content, so the concept of video and
film regions doesn't apply.

The ovr parsing code was stolen from fieldhint and adapted to
vdecimate's needs.
Merge pull request #27 from dubhater/vdecimate-ovr

Override support for vdecimate