#check_signatures name
Add #instances and #outputs getters for SignatureTest
Different API for SignatureTest
More work on SignatureTest(unary signatures)
Predefine some numeric types in a naive way
Add instance inheritance for types
Add definition merging
Use definition merging for #instances and #method_tests of Type
Make #ancestral_instances of Type to be private
Add core_ext
Add basics of Object#type