#68 Improve Exception information in Terser, etc. Javadocs

[DiGiT]

Terser and related classes (MessageNavigator, etc.) Javadocs all say they throw HL7Exception but don't say under what circumstances they throw it. This makes Exception handling hard in my application. Ideally it would throw one Exception for a bad spec string and another if the Primitive for the spec string couldn't be found--and maybe this happens now but it isn't documented. Thanks.

[Christian Ohr]

I'm currently scanning through the codebase to fix code check warnings; this includes missing/incorrect/incomplete javadocs.