Request `body` matcher methods need to allow hamcrest matcher for content-type

[cjstehno]

The Request.body content matcher methods allow for Hamcrest matchers as values, but not for content types. It would be useful (especially in multipart matching) to allow for Hamcrest matchers in the content type fields. So that you could have something like:

expectations {
    post('/foo').body( any(), startsWith('text/') ).responds().code(201)
}

[cjstehno]

The content type is already matched as a starts-with match and it is also used inside of the body content matcher, so this seems like more work than it has value at this point. Shelving for now until there is a real need.