Copied functionality from minimum refinement function plugin.
Added entry to changelog.
Added tests for the maximum refinement function.
Added output from maximum refinement tests.
Create a postprocessor for complete material output.
Better documentation.
Add a line in changes.h
Merge pull request #173 from gassmoeller/material_properties_postprocessor

Create a postprocessor for complete material output.
Function plugins for gravity and boundary temperature.
Fix small bug and improve documentation.
Add tests for function plugins.
Add line in changes.h.
Extended documentation and adjusted default value.
Merge pull request #174 from gassmoeller/function_plugins

Function plugins for gravity and boundary temperature.
Merged changes from master
Merge pull request #153 from jperryhouts/maximum_refinement_function

Maximum refinement function
The heating rate should be a scalar function.
Update minimum refinement function to always read in 3 variables.
Merge pull request #176 from bangerth/fix-default-function

The heating rate should be a scalar function.
Merge pull request #177 from gassmoeller/split_refinement_functions

Workaround for some not working parameter files.