Add elastic constants tools
Add elastic constants tools

This code is from my elastic constants generator
scripts which can be found at:

    https://github.com/andreww/elastic-constants

These should probably be broken out into a seperate
libary to do "MSAT" in Python at sone point. The only
novel thing about these functions is the handling of
errors (including propogation through the matrix
inverse).

andreww/theia_tools