PR: Lattice attributes are always 3D.

[tuopuu]

This PR fixed #80. Please, note that documentation is not modified yet.

Changes:
abstractlattice.py:

• replaced "D x " notation with [3] in docstrings

lattice.py:

• replaced "D x " notation with [3] in docstrings
• factory functions always create 3D Lattices. 2D lattice is embedded on the XY-plane in 3D. This is due to decision by the SSB that the 3rd coordinate is ignored for 2D lattices.
• factory functions still require correct dimensions for lattice parameters, e.g. two dimensions for the size of 2D lattice.

test_lattice.py:

• changed all 2D variables to 3D except in factory functions by adding 0 or 1

h5lattice.py:

• replaced "D x " notation with [3] in docstrings

abc_check_lattice.py:

• tests for 2D-lattices now use 3D attributes

[tuopuu]

@itziakos, @roigcarlo, @kemattil here's the initial push to fix #80. I think there are several ways to implement the SSB decision. This is the one I thought was the simplest. Please, take a look.

There are no try/exceptions written that test the dimensionality of input parameters, but I think they could be added to the factory functions, at least. Please, let me know if you think that's a good idea to do.

[itziakos]

There are no try/exceptions written that test the dimensionality of input parameters, but I think they could be added to the factory functions, at least. Please, let me know if you think that's a good idea to do.

I am in favor of not overdoing it also.

[itziakos]

I think origin should be x, y, z

[tuopuu]

You're right. Docstrings already say that the lattice will be embedded in 3D so the origin must be in 3D.