Fix notebook cvx_examples/circuit_design/clock_mesh

Steven Diamond pointed out a bad double inequality constraint
of the form:

exp <= exp <= exp

which CVXPY will not fail on, but does nothing, so I fixed
this, and upped the number of optimization points to 50
to get results that match the CVX example within a high
degree of precision.
Add example notebook fir_chebychev_design from CVX.

This example was ported from the CVX example "Chebychev design
of an FIR filter given a desired H(w)" by Almir Mutapcic, 02/02/2006.

Porting was done by Judson Wilson, 05/28/2014.

The largest changes were with basic formatting and language conversion,
and necessary changes to convert complex-valued variables into an
equivelent real-valued representation for CVXPY.
Add example notebook l1_trend_filter_snp500 from CVX.

This example was ported from the CVX example "l1 trend filtering"
by Kwangmoo Koh, 12/10/2007.

Porting was done by Judson Wilson, 05/28/2014.

Very little beyond cosmetic changes and porting. Note that ECOS and
SCS return inaccurate results. CVXOPT returns a good result, but
takes a long time, likely due to a bug Steven Diamond mentioned
where CVXOPT treats sparse matrices as full, at the moment.