As of Lua 5.2: "Hexadecimal constants also accept an optional fractional
part plus an optional binary exponent, marked by a letter 'p' or 'P'"
(see at the end of https://www.lua.org/manual/5.2/manual.html#3.1).

The new regexes do not match a leading nor a trailing dot, but they
are good enough.  Discussion on the mailing list:
https://lists.gnu.org/archive/html/nano-devel/2017-12/msg00121.html

Signed-off-by: Tom Levy <tomlevy93@gmail.com>