[ADD/WIP] Add some HTTP request code

We can now *register* users!

src/MatrixError.c

@@ -0,0 +1,17 @@
+#include <Matrix.h>
+
+HashMap *
+MatrixCreateError(char *err, char *msg)
+{
+    HashMap *map;
+    if (!err || !msg)
+    {
+        return NULL;
+    }
+
+    map = HashMapCreate();
+    HashMapSet(map, "errcode",  JsonValueString(err));
+    HashMapSet(map, "error",    JsonValueString(msg));
+
+    return map;
+}