[Tolk] Implement AST: intermediate representation of tolk files

Now, the whole .tolk file can be loaded as AST tree and
then converted to Expr/Op.
This gives a great ability to implement AST transformations.
In the future, more and more code analysis will be moved out of legacy to AST-level.

tolk/ast-from-tokens.h

@@ -0,0 +1,27 @@
+/*
+    This file is part of TON Blockchain Library.
+
+    TON Blockchain Library is free software: you can redistribute it and/or modify
+    it under the terms of the GNU Lesser General Public License as published by
+    the Free Software Foundation, either version 2 of the License, or
+    (at your option) any later version.
+
+    TON Blockchain Library is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU Lesser General Public License for more details.
+
+    You should have received a copy of the GNU Lesser General Public License
+    along with TON Blockchain Library.  If not, see <http://www.gnu.org/licenses/>.
+*/
+#pragma once
+
+#include "src-file.h"
+
+namespace tolk {
+
+struct ASTNodeBase;
+
+const ASTNodeBase* parse_src_file_to_ast(SrcFile* file);
+
+} // namespace tolk