Common base class for HDF related exceptions

[dominikwerder]

Currently, many exceptions thrown by h5cpp can be identified only via inspection of std::runtime_error::what.

A common base type for all exceptions thrown in response to errors originating from libhdf would allow more fine grained error handling.

A further enhancement could be custom exception types for common failure cases, especially those which one can recover from.

[eugenwintersberger]

Good point. We need to discuss this. But you made a point here.

[zjttoefs]

Tobias says this is easy to do.