Disconnect does not allow for 2-byte status code

[Altreus]

I came a cropper of a bug that I debugged like this

--- a/lib/Cro/WebSocket/BodyParsers.pm6
+++ b/lib/Cro/WebSocket/BodyParsers.pm6
@@ -30,6 +30,7 @@ class Cro::WebSocket::BodyParser::JSON does Cro::BodyParser {
 
     method parse($message) {
         $message.body-blob.then: -> $blob-promise {
+            CATCH { say "Not good stuff: " ~ $blob-promise.result.gist }
             from-json $blob-promise.result.decode('utf-8')
         }
     }

The RFC says the first two bytes are an unsigned integer and the rest is whatever.

If there is a body, the first two bytes of the body MUST be a 2-byte unsigned integer (in network byte order) representing a status code with value /code/ defined in Section 7.4. Following the 2-byte integer, the body MAY contain UTF-8-encoded data with value /reason/, the interpretation of which is not defined by this specification.

A websocket I tested with sends non-JSON as reason, but it chokes on decode('utf-8') anyway.

I think close frames should be handled specially but I'm still too novice at this to risk a submission.

[Altai-man]

Test related to #15
as $server.close does not cause internal $!receiver to be closed as well.