add melt material model with latent heat

fix some bugs

indentation

clean up and add documentation

add some documentation

add two tests
add new line
Merge pull request #142 from jdannberg/melting_model

Material model that includes latent heat of melting
Make test compile.
Merge pull request #145 from bangerth/fix-test-using-c++

Make test compile.
fix steinberger test output
Merge pull request #144 from tjhei/fix_steinberger_test_output

fix steinberger test output
update test output (verified, was just forgotten)