Minor documentation updates.
Also remove output files.
Give it a once over.

No functional changes, just updates to documentation and style.
Merge pull request #196 from bangerth/step-52-updates

Step 52 updates
add failing test for ghosted vectors
Allow v=0.0 for ghosted PETSc and Trilinos vectors
Allow v=0.0 for ghosted PETSc and Trilinos vectors
Merge pull request #198 from tjhei/gla_broken_ghost_vec

PETSc and Trilinos vectors with ghost entries can now be reset to zero using = 0.0
Minor doc update.

We had forgotten to update the documentation for the new manifold_id field.
Also a few other touches of TLC.
Merge pull request #199 from bangerth/doc-update-3

Minor doc update for the new manifold_id field.
Update documentation.

The text describing the Solver base class must easily be 15 years old.
I can see 3 Germans writing it, accent, language problems, and all.
More updates.
Merge pull request #200 from bangerth/doc-updates-4

Update documentation.