Changelog for hsndfile-0.4.0

[USER] Simplified Buffer API: A single type class, Buffer, is provided for ForeignPtr based I/O. Instances are provided in separate packages, e.g. hsndfile-vector.

[USER] hsndfile has been adapted to compile with GHC 6.10. The only visible change is in exception handling:
- Sound.File.Sndfile.Exception.Exception is now an instance of Control.Exception.Exception
- The new generalized functions from Control.Exception.Exception are used for throwing and handling exceptions

[BUGFIX] Fix exception throwing Exceptions detected in library code are now actually raised. Exception has been factored into Sound.File.Sndfile.Exception and constructors were added according to the public libsndfile error codes.
[BUGFIX] Fix reading/writing of frames hGetFrames and hPutFrames were using the sample-based library functions. These have been factored into Sound.File.Sndfile.Buffer and the correct functions are being used for the frame-based I/O functions.