Symbolically generate the Fung tangent stiffness
Added short doc to fung_D
Removed exponential factor from fung_D_E.  Faster like this.

Also added a variable to hold the parameters from Holzapfel which are
stable in E(bar).
Fixed reorder_matrix for vectorized, and fixed utri_flat
Fixed subscript error in fung_D
Refactor so the tangent stiffness doesn't need to be computed every time
Remove reference to global stiffness array
Fix pickling of tangent stiffness
Fix typo in lin.minor_dets
Recompute tangent stiffness on any unpickling error
Added numpy, sympy, reload to bench
Need q and f for pickling with fung_D
Matplotlib to bench
Changed E to Ebar.  But is the exp on J right?
Convert float to sympy rational in fung_D
Update symbolics in fung_D
Add optimizations to symbolic expression of D
Require printing to keep status up-to-date
Actually store symbolic computation
Separate symbolic and numeric.  Give everything shorter names.