Document the Ferret "=" operator and improve related documentation
Summary:
Depends on D19529. See PHI778.
- Document the "name" constraint as deprecated. All callers are likely better served by the "query" constraint.
- Guide users toward the "query" constraint a little better.
- Document the = syntax.
Test Plan: Read various new documentation.
Reviewers: amckinley
Reviewed By: amckinley
Differential Revision: https://secure.phabricator.com/D19531