refactored linear operator code so every operator is multiplication by a matrix
finished rewrite of linops
Merge pull request #98 from JudsonWilson/judsons_examples

Judsons examples
Example l1_trend_filter_snp500: Add snp500.txt data.

This is the time series data. Apparently I forgot to commit this.
Add example notebook nonneg_matrix_fact from CVX.

This example was ported from the CVX example "Nonnegative matrix
factorization" by Argyris Zymnis, Joelle Skaf, and Stephen Boyd.

Porting was done by Judson Wilson, 6/2/2014.

Generally this a direct port, with modifications necessary for the
port. For some reason CVXPY will not converge as quickly as
CVX. In fact its possible that the solution will never converge.
I am not sure if this is true. The reason is unclear. It may
be an artifact of the data and the stopping criterion of the solver
at each iteration.
Add example notebook max_entropy from CVX.

This example was ported from the CVX example "Entropy maximization"
by Joelle Skaf, 4/24/2008

Porting was done by Judson Wilson, 6/2/2014.

This is pretty much a straight port.