add chained expectation descriptions to the default descriptions of custom matchers with fluent interfaces

this fixes #532
Rather than using `reset_include_chain_clauses_in_custom_matcher_descriptions_to_default` to put the global config instance into its default state, I'd recommend simply using the [new config instance](https://github.com/oveddan/rspec-expectations/blob/320063ba256150da799b9019a22c7bf2a0ce9503/spec/rspec/expectations/configuration_spec.rb#L6) already available to you.  Since it's a brand new instance, there's no need to call `reset_include_chain_clauses_in_custom_matcher_descriptions_to_default` (or for that method to even exist to support this kind of use case).