History
+2017/08/03: Version 6.5.0
+
+2017/07/30: [new] support Absent clear (Absent functions)
+2017/07/25: abolish configure option: --enable-combination-explosion-check
+2017/07/23: [new] support Absent functions (?~...)
+2017/07/14: fix #65: SIZEOF_SIZE_T doesn't exist on certain architecutres
+2017/07/11: [new] support \O (true anychar)
+2017/07/10: [new] support \K (keep)
+2017/07/10: add new node type: NODE_GIMMICK
+2017/07/07: [new] support \N (no newline)
+2017/07/05: [new] support \R (general newline)
+2017/07/05: [new] support if-then-else syntax
+2017/07/04: [new] support backref validity checker
+
2017/07/03: Version 6.4.0
2017/06/30: fix memory leaks