Use scipy.constants for physical constants.
fix test output
tests: better float comparisons
update tests to use new floating point check
remove annoying output
use numdiff
Add a burnman.constants file to import the scipy constants
Merge pull request #39 from ian-r-rose/offload_constants

Use scipy.constants for physical constants.
Initial working copy (non-functional) adding solid solutions
Adding non-functional solidsolution.py
Abbreviate kd
Add Modified Tait EoS and expression for G
Added molar mass calculator and data table
Minor corrections
Added endmember Gibbs with Landau, and a new test script.
Started work on Bragg-Williams order-disorder.
Continued work on Bragg-Williams order-disorder.
Added minerals to HP_2011.py
Attempts to locate tc-burnman discrepancies
Implemented HP2011 Landau and Bragg-Williams order-disorder models for endmembers