Documents pretty command.
Adds TSet.isValid().
Adds TOrderedSet.isValid().
Moves TSet procs to their code block.
Adds test cases for remaining TSet procs.
Adds TOrderedSet.init(), wraps initOrderedSet around it.
Adds TSet.init(), wraps initSet around it.
Adds more docstrings to the sets module.
Factors common documentation in fragment to avoid repetition.
Adds definition of card term to sets module.
Adds os.copyDirWithPermissions().
Adds hyperlinks to copyFile* docstrings.
Merge pull request #1416 from gradha/pr_copy_dir_permissions

Adds copyDirWithPermissions()
Merge pull request #1412 from gradha/pr_documents_pretty

Documents pretty command.
Merge pull request #1414 from gradha/pr_sets_improvements

Sets improvements