Refactor HTTP serialization and parsing (API Change):

fix #404

Parsing and serialization interfaces have been fine tuned and unified.

For parsing these stream operations are defined:

* read
* read_header
* read_some
* async_read
* async_read_header
* async_read_some

For serialization these stream operations are defined:

* write
* write_header
* write_some
* async_write
* async_write_header
* async_write_some

include/beast/websocket/impl/accept.ipp

@@ -281,7 +281,7 @@ operator()(error_code ec,
 
     case 1:
     {
-        BOOST_ASSERT(d.p.got_header());
+        BOOST_ASSERT(d.p.is_header_done());
         d.ws.stream_.buffer().consume(bytes_used);
         // Arguments from our state must be
         // moved to the stack before releasing

include/beast/websocket/impl/stream.ipp

@@ -96,7 +96,7 @@ do_accept(
         next_layer(), stream_.buffer(), p, ec);
     if(ec)
         return;
-    BOOST_ASSERT(p.got_header());
+    BOOST_ASSERT(p.is_header_done());
     stream_.buffer().consume(bytes_used);
     do_accept(p.get(), decorator, ec);
 }