Closes#797Closes#798
JAXRSContract sets a single Content-Type value
This change allows headers to be cleared by passing a null
value for backwards compatibility.
Multiple Content-Type values are not valid because the body
that we send with any given request will only have a single
type.
Updated header entry assertion to be agnostic to header name
order.
* RequestTemplate.headers clear behavior matches that of query params
* FIXED unsupported jaxrs-2.1 annotations should not break entire interface, resolving #669
* UPDATED jaxrs: more defensive jaxrs2 support
* ADDED jsr311-api dependency to httpclient (as jsr311 is `provided` in feign-jaxrs now)
* UPDATED httpclient `jsr311-api` scope to test
UPDATED jaxrs readme