Make Schema Enumerable.
Move deprecated methods from psych.rb to psych/deprecated.rb.
Few more documentation improvements.
Add Schema#prefix and rename directives to prefixes.
FAILSAFE_SCHEMA does not need to redefine core tags.
Fix legacy tag matching.
* test/psych/test_object.rb: Isolate adding global tags via class.
Document Psych::Set a little better.
Make note on test_spec_legacy_domain prefix test.