Makefile: Added the 'make doc' command.

This command generates the code documentation using Doxygen.
Doxygen: The unit test code is now added to the unit tests group.
Makefile: added the 'docclean' rule.

This rule deletes the generated documentation.
Doxygen: Documented the exception classes.
Doxygen: Added the 'exceptions' doc group.
Fixed a typo in 'groups.dox'.
Doxygen: Added the exception classes to the exceptions doc group.
Doxygen: Added the cameras doc group.
Doxygen: Added the camera classes to the camera doc group.
Doxygen: Documented methods of the UEye_Camera class.
Doxygen: documented the Image class methods.
Makefile: Modified the 'doc' rule.

The documentation is now always regenerated by the 'make doc' command,
even if it was already generated.
Doxygen: added documentation for the utilities test.
Doxygen: minor documentation additions.
Doxygen: Added documentation for the Camera abstract class.
Doxygen: Documented the ImageTest fixture class.
Merge branch 'doc'