version increment

Author: tlk00

src/bmconst.h

@@ -206,7 +206,7 @@ template<bool T> struct _copyright
 
 template<bool T> const char _copyright<T>::_p[] = 
     "BitMagic C++ Library. v.3.20.0 (c) 2002-2019 Anatoliy Kuznetsov.";
-template<bool T> const unsigned _copyright<T>::_v[3] = {3, 18, 0};
+template<bool T> const unsigned _copyright<T>::_v[3] = {3, 20, 0};