add another main goal in the documentation
Merge pull request #9 from tjhei/editmanual

add another main goal in the documentation
Fix forgotten resizing of depth average files. Add an assertion.
Merge pull request #10 from bangerth/fixes

Fix forgotten resizing of depth average files. Add an assertion.
Style fixes.
More style fixes.
Simplify some code. More style fixes.
Style fixes.
More style and documentation fixes.
Merge pull request #11 from bangerth/fixes

Style and documentation fixes
fix .gitignore
Add an interface for an yet to create heating_model in simulator.
Add a heating_model pointer to simulator that gets initialized. Compiles well but no run tests so far.
Add the declare parameters function for heating model interface. Use heating model->radiogenic_heating_rate in assembly.
Add the old radiogenic heating functionality in a new heating model constant heating.
Add a test and a future cookbook for radiogenic heating.
Add a function heating model. set_current_time now gets called at the beginning of a new timestep.
Add a future cookbook for space- and time-dependent radiogenic heating.
Remove parameter Radiogenic heating rate from tests.
Remove parameter Radiogenic heating rate from cookbooks.