Add group documentation to benchmarks and tests.
Fix SpdrBase test failing after recent updates. It now checks passing both valid and invalid paths to setInputPath and setOutputPath.
Expand SpdrImport test, too.
Various additional fixes to SpdrImport tests.
Documentation fixes.
Make SpdrLog official part of libspdr, make it a parent of SpdrBase. Implement SpdrLog signals.
Update the documentation, especially the main page.