Restructure web docs for sparse matrix datastructures #112
Description
We should ...
- Explain how COOMatrix is mostly a data-interchange format. Have a dedicated page on COOMatrix and the free-functions for format conversion.
- Give a page to CSCMatrix. Have it include transpose_as_csr and its implementation of reindex_inplace.
- Give a page to CSRMatrix. Have it include transpose_as_csc and its implementation of reindex_inplace.