pack() and unpack() 64 bit format codes

Hi Internals,

I would like to propose giving pack() and unpack() 64 bit format
codes, mimicking the current behaviour of 32 bit format codes.

Pack and unpack are obviously functions inspired by Perl, which has
the 64 bit format codes 'q' and 'Q'. So the first half of my proposal
is to give pack() and unpack() these options.

q - signed long long (always 64 bit, machine byte order)
Q - unsigned long long (always 64 bit, machine byte order)

Perl does not have format codes to specify endianness, so the second
half of my proposal is to introduce two more format codes for PHP that
behave differently from Perl.

J - unsigned long long (always 64 bit, big endian byte order)
P - unsigned long long (always 64 bit, little endian byte order)

I have chosen these letters _because_ they already exist in Perl,
however their function does not suit PHP. J is for Perl internal
integers, and P is for a pointer to a structure. Both of these are
things that make no sense to support in PHP.

I have ordered them so that J < P in the same way that N < V,
hopefully making it a bit more intuitive for developers to remember
what the codes mean (also P rhymes with V.. kinda)

I don't think this requires an RFC, as it does not break any existing
expected behaviour.

I'd like to hear the lists opinion on introducing these new formatting options.

Provisional PR: https://github.com/php/php-src/pull/812

Cheers,

Leigh.