iterative solver

• Add SELL-C sparse format
• Add a preconditioned conjugate gradient implementation with jacobi preconditioner
• coo2ordered has an optional flag to order also the data which is by default set to false

use fypp for generic meta programming

• Breaking change with respect to previous release: type names changed to facilitate management of real and complex data
• Adoption of fypp as a preprocessor for generic meta-programming

basic classes and kernels for testing purposes

This pre-release contains basic OOP implementations for COO/CSR/CSC/ELL matrices and some kernels