Add r2pipe2.md RFC ##doc

doc/r2pipe2.md

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+# r2pipe2
+
+This document is a draft for the RFC to redesign the r2pipe protocol to cope with all the current limitations. This new protocol must fullfil the following requirements:
+
+* non-blocking command execution
+* capture stderr messages
+* capture logging
+* return code associated
+* extensible with metadata
+
+## Proposal
+
+My proposal consists in defining a new protocol based on JSON, and keep using the well known communication channels we have to send commands and receive output.
+
+When connecting, the first char use to be a null byte on the current r2pipe implementation. Let's name it 'r2pipe1'. In this new protocol the first byte will be an open brace '{'. So the r2pipe1 implementations will be able to detect when they are speaking to an r2pipe2 instance and select the right version of the protocol.
+
+## Handshake
+
+This is a sample communication of this hipothethic r2pipe2 protocol:
+
+>>>>>>>
+```json
+{
+	"protocol": "r2pipe",
+	"version": "2.0"
+}
+```
+
+<<<<<<
+```json
+{
+	"protocol": "r2pipe",
+	"peer": {
+		"name": "radare2"
+		"version": "5.9.0"
+	}
+}
+```
+
+## Running commands
+
+>>>>>>>
+```json
+{
+	"command": "ij",
+	"expect": "text/json",
+	"seqid": 1,
+}
+```
+
+Note that the client requested a json response, so the output is embedded inside the returned document instead of handling it as a string.
+
+The sequence id can be used when running commands in background, this way we can keep track of which is the response of the execution of a command without having to block the client or even execute many commands and wait for them.
+
+<<<<<<
+```json
+{
+	"responses": [{
+		"seqid": 1,
+		"command": "ij",
+		"time": 3824,
+		"logs: "",
+		"stderr": "invalid file",
+		"output": {
+			"core": {
+				"type":"Executable file",
+				"file":"/bin/ls",
+				"fd":4,
+				"size":9488
+			}, "bin":{
+				"arch":"arm",
+				"baddr":4294967296,
+				"binsz":88816,
+				"bintype":"mach0",
+				"bits":64,"canary":true
+			}
+		}
+	}]
+}
+```
+
+## Author
+
+--pancake