Correct StreamType concept in the docs.

Summary:
Resolves #40

{F3809560}

Reviewers: ivica

Reviewed By: ivica

Subscribers: miljen

Differential Revision: https://repo.mireo.local/D37895

Author: biljazovic

doc/qbk/00_main.qbk

@@ -33,6 +33,7 @@
 [template refmem[class mem][reflink2 [class].[mem] [class]::[mem]]]
 [template refmemunq[class mem][reflink2 [class].[mem] [mem]]]
 [template asioreflink[id term][@boost:/doc/html/boost_asio/reference/[id].html [^boost::asio::[term]]]]
+[template asioreflink2[id term][@boost:/doc/html/boost_asio/reference/[id].html [term]]]
 [template beastreflink[id term][@boost:/libs/beast/doc/html/beast/ref/[id].html [^boost::beast::[term]]]]
 [template beastconceptslink[id term][@boost:/libs/beast/doc/html/beast/concepts/[id].html [term]]]
 [template mqttlink[id text][@https://docs.oasis-open.org/mqtt/mqtt/v5.0/os/mqtt-v5.0-os.html#_Toc[id] [text]]]

doc/qbk/reference/concepts/StreamType.qbk

@@ -10,6 +10,15 @@
 
 `StreamType` should meet the [beastconceptslink streams AsyncStream] concept.
 
+[note 
+    Because __WEBSOCKET_STREAM__ does not satisfy [asioreflink2 AsyncWriteStream [^AsyncWriteStream]],
+    requirements were relaxed to allow a stream to provide [*`async_write`] operation instead of [*`async_write_some`].
+
+    With [asioreflink2 ConstBufferSequence [^ConstBufferSequence]] cb and __CompletionToken__ t,
+    [*`s.async_write(cb, t)`] should meet the requirements of an [asioreflink2 asynchronous_operations asynchronous operation] 
+    with the completion signature `void(error_code ec, size_t n)` and should write all the supplied data to the stream.
+]
+
 It should follow Asio's layered stream model by having a `lowest_layer_type` member type,
 and a `lowest_layer` member function, returing a `lowest_layer_type&`. 
 The `lowest_layer_type` should inherit from __TCP_SOCKET__.