Create rapidjsondesign.md

rapidjsondesign.md

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+I looks like RapidJSON can process inputs at 4 cycles per byte. Rapidjson has a function that skips spaces and comments... it is obviously optimized with some SSE... 
+
+Everything else just a series of recursive calls with switch cases. It starts like this...
+
+```
+SkipWhitespaceAndComments<parseFlags>(is);
+ParseValue<parseFlags>(is, handler);
+```
+
+... which is just this...
+
+```
+    void ParseValue(InputStream& is, Handler& handler) {
+        switch (is.Peek()) {
+            case 'n': ParseNull  <parseFlags>(is, handler); break;
+            case 't': ParseTrue  <parseFlags>(is, handler); break;
+            case 'f': ParseFalse <parseFlags>(is, handler); break;
+            case '"': ParseString<parseFlags>(is, handler); break;
+            case '{': ParseObject<parseFlags>(is, handler); break;
+            case '[': ParseArray <parseFlags>(is, handler); break;
+            default :
+                      ParseNumber<parseFlags>(is, handler);
+                      break;
+
+        }
+    }
+```
+
+
+What RapidJSON does not do:
+
+- Lazy evaluation (it figures out the content of strings and numbers)
+- It does not do computed gotos