Add documentation to Collection constraint showing usage of Required
and Optional classes.
Fix missing line breaks and heading line length.
Change complete to completely.
Added configuration-block:: annotation to example section.
Update Collection.rst

Formatting changes per comments from @WouterJ
Update Collection.rst

Change 'example' to 'instance'.
Update Collection.rst

Add variable indicators around profileData
Update Collection.rst

Removed use statements for Required/Optional. Instead use Assert\Collection\Required.
Merge pull request #2432 from afishnamedsquish/collection_constraint_optional_required_docs

Validator Documentation for Collection constraint Required/Optional options