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.
Update a comment.
Merge pull request #201 from bangerth/doc-update-5

Update an error message.
Improved AVX-512 vectorization code path

The original version of the AVX-512 vectorization (DEAL_II_VECTORIZATION_LEVEL = 3) was not properly tested. When I did some tests with gcc, it turned out that I had to fix a few issues. Now it compiles fine and the generated assembler code looks good, but there is no hardware out to test it yet.
I also improved some code comments.
Merge pull request #202 from kronbichler/master

Improved AVX-512 vectorization code path. The original version of the AVX-512 vectorization (DEAL_II_VECTORIZATION_LEVEL = 3) was not properly tested. When I did some tests with gcc, it turned out that I had to fix a few issues. Now it compiles fine and the generated assembler code looks good, but there is no hardware out to test it yet.
Added set_matrix_mode to the SLEPcWrappers::TransformationBase class.
Fix a test.

We have recently allowed that one can set a vector to zero, even if it has
ghost elements. But this test verified that we throw an exception in this
case. Remove this one test.
Also ensure that we have ML as part of Trilinos.
Merge pull request #208 from bangerth/augment-trilinos-detection

Also ensure that we have ML as part of Trilinos.
Merge pull request #207 from bangerth/fix-test

We have recently allowed that one can set a vector to zero, even if it has
ghost elements. But this test verified that we throw an exception in this
case. Remove this one test.
Remove part of a test.

The test verifies that it doesn't matter whether we first call
DoFHandler::distribute_dofs() and then DoFHandler::distribute_mg_dofs(),
or the other way around. But we have recently changed the behavior
to require exactly this order, so this part of the test is no longer of interest.
Merge pull request #206 from bangerth/remove-faulty-test

The test verifies that it doesn't matter whether we first call
DoFHandler::distribute_dofs() and then DoFHandler::distribute_mg_dofs(),
or the other way around. But we have recently changed the behavior
to require exactly this order, so part of the test is no longer of interest.
Disable nonlocal graph in Trilinos sparsity pattern because Trilinos has a bug.
Merge pull request #209 from kronbichler/master

Disable nonlocal graph in Trilinos sparsity pattern (revisit in 11.13)
document project_boundary_values_div_conforming better
spell check, minor edits
wrap comments
Merge pull request #210 from tjhei/documentation_fixes

Documentation fixes