== and != functionality for CSC and CSR sparse matrices

Add support for == and != comparisons for CSC and CSR sparse matrices. Currently broadcasting comparisons with sparse matrices is not supported, but comparisons with broadcastable dense matrices, and scalars is. Comparing a sparse matrix with a dense matrix returns a dense result.

Build time and memory usage on this branch: 75.63 seconds, 440.6 MB
Bulid time and memory usage on master: 67.6 seconds, 438.2 MB

A 12% increase in build time, might be significant.