3.0.0 Comprehensive library restructuring

This is a general restructuring of the library.
In particular:

• inheritance is now used extensively
• the definition of models and corresponding masks for parameters is much more consistent now
• several simulation models testing individual EHTPlib models have been added. This helps users use the provided models, since they can see the expected behaviour at least in some cases.
• the companion library EHPTexamples is also updated, and its tutorial, which is also tutorial of EHTPlib, has grown from 78 pages to 124.

2.1.4 First public release

This is the first public release of the library.
This library, however, was first introduced in 2014, so it is already rather mature.