Basic search for multiple reference frames
Fixed some of the motion vector scaling problems

motion vector candidates are not yet scaled or selected correctly
Simplified MV scaling calculations
Fixed inter mv_ref propagation and merge candidate mv_ref matching
Fix for MV candidate derivation
Fixed deblocking filter when using multiple reference frames
Fixed merge candidate selection on multiref
Fixed mvd candidate selection
Added commandline parameter for reference frame number

Also updated README and usage with the new parameter
Merge branch 'multiref'