fix solution for binary_gray

I'm not sure what binary_gray was doing, but I don't think it was doing
it right.  It should work now as intended.

Also fixed spelling of Gray.
update solutions

The QR was incorrectly calculated.
reorganized QR explanation

Added a problem to use QR to calculate the determinate.
revisited least squares with QR.

Use triangular solver instead of inverting R.  Updated solutions.
rename QR tex file
talk about pivoting
add QR least squares problem

Use QR decomposition to computer solutions to least squares problems.
remove section on pivoting

Also added comments to solutions file.
Merge pull request #324 from ayr0/qr

Added problems related to QR and least squares using QR.
Merge pull request #314 from ayr0/generators

fix solution for binary_gray
remove maze problem

Removed maze problem because it was not clearly beneficial to student's
learning.  It was essentially a really convoluted version of breadth
first search.
Merge pull request #323 from abefrandsen/develop

Made some edits to the vectorization lab.
add problem to calculate Laplacian matrix of simple graph.
Merge pull request #328 from ayr0/markov

Markov lab edits
Merge branch 'develop' of https://github.com/byuimpact/numerical_computing into develop