doc: add datatypes.

Change-Id: Ia8e3903d619f733cd2951945a2a2bbc8d883b3e7

doc/source/protocol/datatypes.rst

@@ -0,0 +1,77 @@
+Datatypes
+=========
+
+.. list-table::
+    :header-rows: 1
+
+    * - Data type
+      - Specification (simple)
+      - Specification (with limits)
+      - Transport example
+      - Datatype used in C/C++ API
+      - Remarks 
+
+    * - double
+      - ["double"]
+      - ["double", <min>, <max>]
+      - 3.14159265
+      - double
+      -  
+
+    * - int
+      - ["int"]
+      - ["int", <min>, <max>]
+      - -55
+      - int64_t
+      -
+
+    * - bool
+      - ["bool"]
+      -
+      - true
+      - int64_t
+      -
+
+    * - enum
+      - ["enum", {<name> : <value>, ....}]
+      -
+      - 1
+      - int64_t
+      -
+
+    * - string
+      - ["string"]
+      - ["string", <min len>, <max len>]
+      - "hello!"
+      - char *
+      -
+
+    * - blob
+      - ["blob"]
+      - ["blob", <min len>, <max len>]
+      - "AA=="
+      - struct {int64_t len, char \*data}
+      - transport is base64 encoded
+
+    * - array
+      - ["array", <basic type>]
+      - ["array", <basic type>, <min len>, <max len>]
+      - [3,4,7,2,1]
+      - <basic_datatype>[]
+      -
+
+    * - tuple
+      - ["tuple", [<datatype>, <datatype>, ...]]
+      -
+      - [0,"idle"]
+      - struct ??
+      - 
+
+    * - struct
+      - ["struct", {<name> : <datatype>, <name>: <datatype>, ....}]
+      -
+      - {"x": 0, "y": 1}
+      - struct ??
+      -
+      
+

doc/source/protocol/index.rst

@@ -12,6 +12,7 @@ Protocol documentation
    modsubset
    heartbeat
    jsonstruct
+   datatypes
    todo
    notes
    history