Added StaticJsonDocument and DynamicJsonDocument.

Removed StaticJsonArray and DynamicJsonArray.
Removed StaticJsonObject and DynamicJsonObject.
Removed StaticJsonVariant and DynamicJsonVariant.

test/JsonObject/get.cpp

@@ -8,7 +8,8 @@
 using namespace Catch::Matchers;
 
 TEST_CASE("JsonObject::get()") {
-  DynamicJsonObject obj;
+  DynamicJsonDocument doc;
+  JsonObject& obj = doc.to<JsonObject>();
 
   SECTION("GetConstCharPointer_GivenStringLiteral") {
     obj.set("hello", "world");