Improving NMatrix: Adding features to NMatrix core

NMatrix is being re-implemented by SciRuby contributors here at https://github.com/prasunanand/nmatrix_reloaded. This re-implementation is having a fast core written using C-API with Ruby front-end. With this project, we aim to create a faster NMatrix which will replace the original NMatrix later on and the source would be simpler and easier to read and improve. This proposal is to add more features to this newer NMatrix such as adding support for LAPACK and BLAS routines, sparse matrix operations, indexing and broadcasting, matrix decomposition etc.