Fixed support for upper/lower x bounds.

Previously wasn't working - now it is. The problem tests also properly checks
for it. Also, now correctly implements primal-dual method.
Added solver code.
Changed to reflect shift to SQP algorithm.

Moved original interior-point code to a nitro submodule. Updated README w/
above shift, and added more references. QP code to be added next.
Significant changes.

Moving to a SQP algorithm (even though the package is PyIntropt for interior
point methods). Many changes reflecting this; right now, have implemented an
active-set QP solver.
QP solver somewhat working.

The QP solver seems to be working, and has limited feasibility handling, but
still has a significant cycling issue.
QP solver works, with some feasibility.

Still lacks robustness, but works "better" than previously.
Minor refinements to QP, added initial SQP

The S-C approach made the QP solver slower, so now it just is doing a direct
solve. Following this commit, the dense option is going to go away - it's not
worth the headache of maintaining two pathways.

The SQP solver has been coded but not thoroughly tested. "Stalling" in the QP
solver is preventing this. Next steps are fix stalling w/ perturbation of
bounds, remove dense option, and (possibly) investigate null space method for
QP solver.
QP solver seems in better shape.

Some anti-stalling perturbation method in place.
Could probably be more robust.
The sparse solve is also looking a little weak sometimes, now...
SQP solver needs additional work.
A in-between step, fixing linear constraint dep

I believe a function (which is very slow) in qp_solver needs to be uncommented
for this to work again, but it is very slow, so changes are being made.
Added code for QR decomposition
Integration of dependent row removal using QR

The code to elimante dependent rows using the (wrapped) SparseSuite QR
decomposition it now in (and apparently, it works).

There still seems to be weakness with ill-defined SQP problems, although QP
problems seem to be doing OK.

Implementation of Bett's relaxation strategy is probably the next step.