Feature mesh

Dear all,
Here is the implementation of the stand-alone mesh.
Files:
 - abstractmesh.py: abstract interface for the class
 - mesh.py: current implementation of the mesh and the different types of elements.
 - test_mesh.py: the set of unitary tests for the class.

Please be wellcome to review the code and point out any suggestion or improvement.
Br. 

I agree that it needs to be referred either **id** or **uuid**. Although, I would like to use  **uuid**. It will reflect that the value has to be unique, and I believe that ( correct me if I am wrong ) id() is a built-in function and perhaps is a good idea not using  the same name in order to avoid conflicts 

As for the Parameters I understand from the numpy documentation that it should be located in the class docstring, instead of __init__:

https://github.com/numpy/numpy/blob/master/doc/HOWTO_DOCUMENT.rst.txt#class-docstring