code style: whitespaces

also added a few STDLIB includes for better symbol lookup
sweeper: better names for function evaluations
adding 'override' identifier where valid

there are two advantages of using the 'override' identifier on member
functions:
1. the compiler will raise an error if a method one thinks is overriding
   another one but isn't
2. users will instantly see where a method is overridden
sweeper: rename f_solve to impl_solve
add UNUSED(expr) makro to denote unused parameters

The issue with commenting out parameter names in function definitions is
that those cannot be properly be documented with Doxygen.
To omit compiler warnings about unsued parameters, one should write

(void)(param);

in the function body.
For ease of use and readability, a makro for this is defined similar to
the one defined by the Qt project (Q_UNUSED):

UNUSED(param);
sweeper: cleanup of IMEXSweeper

This mainly rewamps naming of variables to comply with recent
developments in mathematical notation of SDC and PFASST.

I've also added a bunch of documentation especially for the non-trivial
modification of the S matrix to save some additions in each iteration.
We should discuss, whether this modification (which is yet nowhere
explained) is required in a showcase implementation of SDC.
further documentation for interfaces
examples: some docu and variable renaming for the AdVecSweeper

Variable renaming mainly to stick with resent mathematical notations.
doc: Fix explanation of `impl_solv`.
Untabify.
Merge pull request #2 from memmett/memmett/code-cleanup

Fix docs for `impl_solve`.
renaming a few variables

as suggested by @memmett
tests: Add test_mpi_advection_diffusion.cpp.

This implements a basic test for the MPI-PFASST version of the
advection/diffusion example.
Merge branch 'development' into feature/test-mpi
tests: Update expected solutions and tighten tolerances.
test: Loosen tolerances.
Merge remote-tracking branch 'tobbe/feature/code-cleanup' into memmett/code-cleanup

Conflicts:
	include/pfasst/encap/encap_sweeper.hpp
	include/pfasst/encap/imex_sweeper.hpp
	include/pfasst/interfaces.hpp
Merge pull request #3 from memmett/memmett/code-cleanup

Merge development into code-cleanup.
a couple of code formatting tweaks
Merge pull request #57 from memmett/feature/test-mpi

Add test for MPI version of advection/diffusion example.  This closes #41 as well.