Fixed bug in print_dense_jacobian()
Corrected the continuity physics residual

It was using the shear modulus as the coefficient instead of the
bulk mod.
Peridynamics Mixed Newton

An attempt at resolving the convergence difficulty of the mixed
form of peridynamics by computing the jacobian by Newton's method
rather than finite differences. Doesn't seem to help the convergence
at all.
Full Coupling Physics and Completed Mixed Form

The mixed form is completed (pointwise enforcement of continuity)
and has been tested for a coupled problems like Cooke's and the
Newton problem. The full coupling is very rudimentary and needs a lot
of work. This commit was basically a trial to see if full coupling
would get the mixed method to converge. Turns out it works well.
Another formulation for continuity is needed since the results are
almost identical to the non-mixed form (still shows locking). This
is more or less a place holder commit to come back to later and
fix up the code.

The management of the coupling could be a lot better, but at least
this proves that the user can select between a number of coupling
schemes to try and solve problems. More work needs to be done to make
this more seamless.
Mixed form, another version of continuity

This version of the continuity equation enforces the p=-ktheta relationship
over all the neighbors in a neighborhood. The resulting stiffness matrix
is not symmetric. This is also a work in progress, but it doesn't effect
the rest of the code.

Note: In order to make the previous continuity version to work, you have
to add back in the symmetric terms in the stiffness matrix (they have
been commented out because this version is not symmetric)
Added more support for PYRAMID5 elements and a test