Assess/revise exceptions hierarchy

[thebigmunch]

• Do we need all these specific exceptions? If not, what do we need?
• Should the exception categories be rethought/reorganized/generalized?
• Just use one exception class?

[thebigmunch]

So, I think the best thing to do to start is to strip everything down to a small number of generic exceptions:

• AudioMetadataException - The base exception for all exceptions deriving from audio-metadata.
• UnsupportedFormat - The exception raised when encountering a file format not supported by audio-metadata. This includes formats that are generally supported, but a specific version or profile of that format is not supported.
• FormatError - The exception raised when the binary format of the file is invalid in some way. This would encompass the previous exceptions:
  • InvalidBlock
  • InvalidChunk
  • InvalidFormat
  • InvalidFrame in the context of MPEG frames, and invalid binary format of ID3v2 frames.
  • InvalidHeader
• TagError - The exception raised when there is an issue with a tag not related to the binary format. For example. an ID3v2 TYER frame containg an ISO-8601 datetime instead of just a year. This might be changed to a warning in Add strict/lenient modes with toggles #18.

Adding any more exceptions or adding arguments to these exceptions can be discussed as potential needs arise.