Various issues in the "Signature for mp3 without id3" algorithm

[Wuelle]

Link to the algorithm in question.

• the mp3-rates table and mp2.5-rates table do not contain index = 15, but the algorithm allows for this value (index is 4 bits)
• the sample-rate table does not define a value for index = 3. match an mp3 header contains a check that bails out if index is 3, but parse an mp3 frame does not.
• parse_mp3_frame computes a samplerate that is never used
• Typo: 6. Let skipped-bytes the return value of [...] -> 6. Let skipped-bytes be the return value of [...]
• I'm not too familiar with the way this is handled in other specs but IMO expressions like sequence[s + 1] & 0x06 >> 1. should contain parenthesis, as the order of operations is not immediately obvious. (this might come down to personal preference)