fixed windows warning
removed SYMMETRISE ifdef and bicgstab solver
broke solver out into a separate class
Removed old conjugate_gradients method
Added new ConjugateResiduals class

not implemented yet...
Housekeeping

made a ConsituativeModel abstract class and subclassed it to
SnowConstituitiveModel for all the snow specific stuff, and replaced
some silly ifdefs with member variables on the Grid or the
SnowConstituitiveModel.
Constituitive model can now control plasticity
implemented conjugate residuals

I think...
Removed unwanted stuff from ConjugateGradients
Switched back to CG, updated test code
Added Preconditioner class in case I need it
Made implicit update code a bit clearer
More fiddling
Given the matrix better eigenvalues!

done a bit of funky transformation shenanigans to move the masses off
the main diagonal - now the conjugate gradients solver converges way
faster
added some comments
Added preconditioner header to project

I should probably move that remapping shiz into a preconditioner
shouldn't I, seeing as it is basically a preconditioner, and it'll make
the code easier to read...