Updates to various places of the documentation.
Test lac/SchurMatrix
Test lac/SchurMatrix; Indented
Merge pull request #165 from dakshinai/test_schur_matrix

Add tests for class SchurMatrix
Adjust based on Guido's feedback.
Merge pull request #164 from bangerth/doc-fixes-8

Updates to the documentation of the quadrature formulas.
Augment documentation motivated by Martin's post on the mailing list.