interfaces: Pass ICommunicator to send/recv.
mpi: Add mpi_communicator.hpp and mpi_vector.hpp.
pfasst: Add pfasst.hpp.
mlsdc: Fix IMEX sweeper to get MLSDC working again.

Signed-off-by: Matthew Emmett <memmett@gmail.com>
DEBUG: echo mag of q in f1eval.
Merge branch 'feature/mpi-pfasst' into feature/mpi-pfasst-development

Signed-off-by: Matthew Emmett <memmett@gmail.com>

Conflicts:
	examples/advection_diffusion/advection_diffusion_sweeper.hpp
	include/pfasst/encap/encap_sweeper.hpp
	include/pfasst/encap/encapsulation.hpp
	include/pfasst/encap/imex_sweeper.hpp
	include/pfasst/encap/poly_interp.hpp
	include/pfasst/encap/vector.hpp
	include/pfasst/interfaces.hpp
	include/pfasst/pfasst.hpp
controller: Use `int` instead of `size_t` in `LevelIter`.

This make the following work properly:

    for (auto l = this->finest()-1; l >= this->coarsest(); --l)

Signed-off-by: Matthew Emmett <memmett@gmail.com>
interfaces: Add `initial_only` flag to `save`.

Signed-off-by: Matthew Emmett <memmett@gmail.com>
poly_interp: Add `restrict_initial_only` flag to `restrict`.

Signed-off-by: Matthew Emmett <memmett@gmail.com>
send/recv: Add `tag` and `blocking` flags to send/recv.

Signed-off-by: Matthew Emmett <memmett@gmail.com>
mpi/pfasst: Flesh out MPI send/recv.

Signed-off-by: Matthew Emmett <memmett@gmail.com>
Merge branch 'feature/state' into feature/mpi-pfasst-development

Signed-off-by: Matthew Emmett <memmett@gmail.com>

Conflicts:
	examples/advection_diffusion/advection_diffusion_sweeper.hpp
interp: Add interp_initial_only flag.

Signed-off-by: Matthew Emmett <memmett@gmail.com>
mpi_vector: Call MPI_Wait when doing a non-blocking send.

Signed-off-by: Matthew Emmett <memmett@gmail.com>
pfasst: Get PFASST working.  Needs to be flensed.

Signed-off-by: Matthew Emmett <memmett@gmail.com>
Merge branch 'feature/mpi-pfasst-development' into feature/mpi-pf

Signed-off-by: Matthew Emmett <memmett@gmail.com>

Conflicts:
	include/pfasst/controller.hpp
	include/pfasst/encap/encapsulation.hpp
	include/pfasst/encap/poly_interp.hpp
style: Tidy and silence some compiler warnings.

Signed-off-by: Matthew Emmett <memmett@gmail.com>
pfasst: Update loops to use new controller state routines.

Signed-off-by: Matthew Emmett <memmett@gmail.com>
controller: Revert back to `size_t` instead of `int`.

This was an inadvertent regression.

Signed-off-by: Matthew Emmett <memmett@gmail.com>
style: Untabify.

Signed-off-by: Matthew Emmett <memmett@gmail.com>