V4: add a boolean matcher

[uglyog]

Using type matchers with headers and query parameters is useless, as the values are always strings. See pact-foundation/pact-jvm#1346. There are already specific matchers for numbers and date values from V3.

This adds a boolean matcher that will match any boolean value, or the string values 'true' and 'false'. That way you can write more intuitive DSLs than just using regex macthers.