Add an audio emphasis element (v5) to mark some tracks

[robUx4]

Fixes #582

• The reserved values is added so that the first 4 values match the MPEG Audio header.
• The phono values are taken from this detailed document. Only the curves using 3 time constants (as the RIAA) ones are kept (1950 and up, before it's too messy)
• I couldn't find a proper RIAA document with the equation but there's a NAB document with the same values and the equation available.
• The CCITT J.17 is actually T-REC-J.17
• I could not find a proper spec for the FM time constants, even Wikipedia doesn't mention any.