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.
When I escape them under R16 the whole string is represented as a list of unicode characters, without escaping it parses it as a list of bytes and that's why it works with list_to_binary.
I'm using the \x{} syntax. For now I don't have any other idea.