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

this fixes #532
@myronmarston I tried this, but getting the failed tests:
default positive expectation failure message that does not include any of the chained matchers' descriptions

```
Failure/Error: expect { matcher.matches?(2) }.to fail_with 'expected 2 to be bigger than 5'
expected RSpec::Expectations::ExpectationNotMetError with "expected 2 to be bigger than 5" but nothing was raised
```

What am I doing wrong?