History
+2017/12/26: Version 6.7.0
+
+2017/12/05: restructure StackType
+2017/11/13: implement subexp calls (?R), (?&name), (?-n), (?+n) for Perl syntax
+2017/09/25: use string pool of gperf for Unicode Property lookup function
+2017/09/16: fix #70: an empty greedy regex and a word boundary (.*\b) fails
+2017/09/13: remove a stack type STK_POS
+2017/09/08: fix #69: add a declaration of onig_end()
+2017/09/07: fix #68: Compilation failure in out-of-source build
+2017/09/03: [new] hexadecimal codepoint \uHHHH
+
+2017/08/30: Version 6.6.1
+
+2017/08/29: fix definition of \X to (?>\O(?:\Y\O)*)
+
2017/08/28: Version 6.6.0
+2017/08/26: fix #67: can't compile with Visual Studio 2005
2017/08/24: rename Absent clear to Range clear
2017/08/21: [new] Extended Grapheme Cluster \X and boundary \y, \Y
2017/08/17: fix: invalid index(ctype) value assigned to Unicode Block properties