Check headers

[rkclark]

After much pain this is the suggested API:

• requestedWith - exact match on body
• requestedWithHeaders - exact match on headers
• requestedWithHeadersMatch - fuzzy match on headers

Reason for not providing fuzzy match on body is that body can be many different types (e.g. string, obj, array) and it is too complicated to add given that we don't have a requirement for it.