Add a picture to show what an option does.
Merge pull request #214 from bangerth/extend-documentation

Add a picture to show what an option does.
Fix a typo.
Merge pull request #215 from bangerth/extend-documentation-2

Fix a typo.
adjust a default value to account for the use of a different temperature in the original source of the melting model
Merge pull request #216 from jdannberg/melt_fraction_fix

adjust a default value to account for the use of a different temperature in the original source of the melting model.

I just noticed that in the Sobolev et al (2011) paper they use the potential temperature instead of the absolute temperature. This means they do not consider the adiabatic temperature change and their melting temperature is lower compared to the one that should be used in a model with the "real" temperature.
Use a trick by Martin Kronbichler to accelerate matrix operations in parallel.

This tells deal.II to use a structure on the side to facilitate faster writing into
matrices when doing computations in parallel.
These should be lowercase.
Add a check to avoid this bug.
Merge pull request #217 from bangerth/accelerate-sparsity-pattern

Use a trick by Martin Kronbichler to accelerate matrix operations in parallel
Make sure <link.h> exists before using it.
Merge pull request #219 from ian-r-rose/fix_typo

Fix bug in multicomponent
fix test output

some differences were introduced in the multicomponent* tests and the other tests
 changed due to some configuration change.
Merge pull request #220 from bangerth/verify-link.h-existence

Make sure <link.h> exists before using it.
Merge pull request #221 from tjhei/fix_tests

fix test output