Add proxy functionality description.

docs/proxy_description.txt

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+Description of the WebSockets to TCP Proxy
+
+
+At the most basic level, the proxy just translates WebSockets traffic
+to normal socket traffic. The proxy accepts the WebSockets header,
+parses it, and then begins forwarding traffic between the client and
+the target in both directions.  At a minimum the proxy needs to base64
+encode traffic destined for the client and decode it coming from the
+client. Also, WebSockets traffic starts with '\0' (0) and ends with
+'\xff' (255) so that needs to be added/stripped by the proxy.  There
+is a little bit of buffering you need to do in case the data from the
+client isn't a full WebSockets frame (i.e. doesn't end in 255).
+
+
+Other proxy features (that aren't necessary for the basic operation):
+
+
+SSL (the wss:// WebSockets URI):
+
+This is detected automatically by the proxy by sniffing the first byte
+of the client's connection and then wrapping the socket if the data
+starts with '\x16' (indicating SSL).
+
+
+Sequence Numbering:
+
+When the client doesn't have native WebSockets support in the browser
+(currently only Chrome and Safari 5), a flash emulator fallback is
+used.  Unfortunately, when this is used, frame ordering is not 100%,
+so the GET URI in the initial handshake has "seq_num=1". This tells
+the proxy to add sequence numbers to every WebSockets frame so that
+the browser can reorder them.
+
+
+UTF-8 encoding:
+
+In addition to the base64 encoding of the data, the proxy also
+supports UTF-8 encoding of the data (the native WebSockets encoding).
+However, in order to not burden the browser too much, the encoding
+doesn't use the full UTF-8 value space, but only uses the first 256
+values. This actually makes UTF-8 encoding slightly less space
+efficient than base64. Also, flash cannot handle byte arrays with 0's
+in them properly, so the values are actually 1-256 (rather than 0-255)
+and the browser does modulus 256 on the data. For these two reasons,
+base64 is the default and is indicated in the GET string by
+"base64=1".
+
+
+Flash security policy:
+
+The proxy detects flash security policy requests (again by sniffing
+the first packet) and answers with an appropriate flash security
+policy response (and then closes the port). This means no separate
+flash security policy server is needed for supporting the flash
+WebSockets fallback emulator.
+
+
+Daemonizing:
+
+The proxy also supports daemonizing (when the -f option is not
+specified).
+
+
+Record:
+
+Finally, there is a debug feature that allows recording of the traffic
+sent and received from the client to a file (the --record option).