codec/h264/h264dec/cavlc.go: combine level and run information

[Saxon Milton]

Implement process to combine level and run information as described by section 9.2.4 as follows:

Input to this process are a list of transform coefficient levels called levelVal, a list of runs called runVal, and the number
of non-zero transform coefficient levels TotalCoeff( coeff_token ).

Output of this process is an list coeffLevel of transform coefficient levels.

A variable coeffNum is set equal to −1 and an index i is set equal to TotalCoeff( coeff_token ) − 1. The following ordered
steps are then applied TotalCoeff( coeff_token ) times:

1. coeffNum is incremented by runVal[ i ] + 1.
2. coeffLevel[ coeffNum ] is set equal to levelVal[ i ].
3. The index i is decremented by 1.

[Saxon Milton]

Addressed in PR #246