Add rspec matchers for cassandra statements #30
Description
expect(query.statement).to have_cql_assignment(:field)
expect(query.statement).to have_cql_assignment(:field, value)
expect(query.statement).to have_cql_relation(:field)
expect(query.statement).to have_cql_relation(:field, value)
Would go a long way for clients to be able to stop their testing plane sooner and have faster cassandra query coverage.