Added a discid_read_sparse() method.

This allows faster reading of  a disc when some features, e.g. ISRC or MCN, are not required.
Added example for discid_read_sparse()
The features flag parameter should be an unsigned int.
Small documentation fixes.
By default discid_read will use all available features.
Updated existing examples to use discid_read_sparse(), removed separate example discid_sparse.c.
Merge remote-tracking branch 'phw/read_sparse'

See LIB-29 and pull request #11
better coding style in darwin disc_read

Only fixing that one function, since it was recently changed a bit,
so we have consistent style at least in the function.
Other fixes should be made with other code changes.

I am not necessarily fond of tab indentation, but that is
what the main files are using.
update AUTHORS and ChangeLog for read_sparse