Added inverse element dictionary and 2d/3d class.
Refactored to read keyword style

Before we read line by line and had a state for what we are currently
reading. Now it uses the keywords to determine what read function that
should be called.
Updated to work with dictionary

And removed 2d/3d distinction.
Removed 2d/3d distinction
Removed tetra from element class
Removed poly, added dimension variable.
Removed 2d/3d distinction
Fixed indentation
Updated test for export
Updated test to work with removed 2d/3d distinction