ICU 66 updates to Unicode 13, including new characters, scripts, emoji, and corresponding API constants. It also updates to CLDR 36.1 with Unicode 13 updates and bug fixes.

Create symbolic link to current version.

FIX CVE-2020-10531
 An integer overflow, leading to a heap-based buffer overflow, exists in the UnicodeString::doAppend() function in common/unistr.cpp.

Signed-off-by: Hirokazu MORIKAWA <morikw2@gmail.com>