Implemented partially joinRoomHandler function.
Added tests on empty username and room_id parameters, response content type, error messages.
Added tests on response message content and status code if room not found.
Implemented if room does not exist.
Implemented if room does not exist.
Merge branch 'join-room-handler-tests' of https://github.com/mownier/moanhermes into the local branch 'join-room-handler-tests'
Conflicts:
	server/server.go
Added test when already joined user tries to join again.
Implemented if user is already joined.
Added test on successfully joined user.
Implemented successfully joined user.
Considered a loop in finding the test room.
Merge branch 'join-room-handler-tests' into development