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

this fixes #532
This is what I currently have but it seems overly verbose:
```ruby
context "with include_chain_clauses_in_custom_matcher_descriptions configured to true" do
          before do
            RSpec.configure do |config|
              config.expect_with :rspec do |c|
                c.include_chain_clauses_in_custom_matcher_descriptions = true
              end
            end
          end

          after do
            RSpec.configure do |config|
              config.expect_with :rspec do |c|
                c.include_chain_clauses_in_custom_matcher_descriptions = nil
              end
            end
          end

          it "provides a default description that does includes the chained matchers' descriptions" do

            expect(matcher.and_divisible_by(10).description).to eq 'be even and divisible by 10 and divisible by 10'
          end
        end
```