"__repr__()" Method ("_lbh15.py") Improvement

[lelaus]

• [1] add the pressure to the variables to print;
• [2] typically, the __repr__() method should return a string that represents the Python instruction to use for re-instantiating the instance it is called on; currently, its purpose is to provide a concise description of the instance it is called on; how to interpret the method?

[panDanieleN]

The first task handled in #106.