Rewarite core with an AST for statements and RPN for expressions (#149)

* test

* improve ast

* add if statement

* shunting-yard start

* renderer as node visitor

* improve ast

* improve ast further

* first functions

* improve ast v3

* improve ast v4

* fix parser error location

* nested ifs

* fix comma, activate more tests

* fix line statements

* fix some more tests

* fix callbacks without arguments

* add json literal array and object

* use switch in expression

* fix default function

* fix loop data

* improved tests and benchmark

* fix minus numbers

* improve all

* fix warnings, optimizations

* fix callbacks argument order

* dont move loop parent

* a few more test

* fix clang-3

* fix pointers

* clean

* update single include

test/test.cpp

@@ -0,0 +1,15 @@
+// Copyright (c) 2020 Pantor. All rights reserved.
+
+#define DOCTEST_CONFIG_IMPLEMENT_WITH_MAIN
+
+#include "doctest/doctest.h"
+#include "inja/inja.hpp"
+
+using json = nlohmann::json;
+
+const std::string test_file_directory {"../test/data/"};
+
+#include "test-files.cpp"
+#include "test-functions.cpp"
+#include "test-renderer.cpp"
+#include "test-units.cpp"