Transform list of unicode chars in templater

Since OTP 17 strings read from a file are by default parsed as a list of
unicode characters.
If such a list contains a non-ascii character (unicode > 255) then a
call to erlang:list_to_binary/1 fails.
This commit converts unicode list of chars to binary via unicode module
if ran against OTP >= 17.
So we cannot escape it? Might be worth asking on erlang-questions regardless of this patch.