add chained expectation descriptions to the default descriptions of custom matchers with fluent interfaces
this fixes #532
Added RSpec::Matchers.configuration.include_chain_clauses_in_custom_matcher_descriptions that
when set to true, custom matcher descriptions and failure messages will include clauses from
methods defined using `chain`.

Fixed some code to match the naming conventions

Fixes #532
Merge pull request #600 from oveddan/chained-matcher-descriptions

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