[refactor] [test] Http/Headers::getHeaders() returns all headers if no field name provided
[refactor] [test] InvalidVerbException now a subclass of InvalidArgumentsException
[comment] typo
[add] [rest] missing base Message methods: setVersion(), getVersion(), getHeadersContainer()
[add] [test] Request constructor
[add] [test] missing Response methods: setStatusCode(), setReasonPhrase(), getReasonPhrase() and a constructor
[add] exception classes for when header container is missing, when provided status code is invalid and when message version is invalid
Merge branch 'develop'
[add] [test] missing methods Response setContent() and getContent() and refactored constructor to take content as first optional argument
[refactor] [test] Message, Request and Response now have their own namespaces in Http; Message content is now an instances of some class that implements ContentInterface
[add] [test] Content\Text
Merge branch 'develop'
[add] [test] responses as stream
Merge branch 'develop'