Output solution as a MATLAB function.

This way, we can run the example as

    ./sim_simple | sed -n '/s1 *=/,$p' > solution.m

to obtain a MATLAB function containing the 'solution'.
Merge remote-tracking branch 'atgeirr/master'

Conflicts:
	sim_simple.cpp
Fix mismerge.
Minor refactoring of UpwindSelector.

Also rename -> UpwindSelectorTotalFlux.