Provides amgcl::backend::map() for ublas::compressed_matrix and allows
  to use ublas vectors with builtin backend.
* Moved make_solver parameters into single params struct
  This is an API breaking change!
  This unifies treatment of amg and solver params in amgcl::make_solver,
  amgcl::runtime::make_solver, and amgcl::mpi::subdmain_deflation classes.
  Now, whenever a class contains both an amg hierarchy and an iterative
  solver, the amg parameters may be accessed through the class
  params::amg, and the solver parameters -- through params::solver.
* Fixed pyamgcl for use with python3 and arch linux.