Add messages for raised errors

[hayfield]

At a number of points throughout the library, raise [Error] is used without a specific message.

The initial idea was to use a combination of the logging mechanism and raising an error with a message. This was slightly put on hold when realising errors need properly looking at.

This is something that can be done in the interim before errors are properly looked at in full.

[hayfield]

#240 is an issue for looking at the wide design issue of errors and exceptions.