sys: [Windows] use more precise timing and sleeping

sys: [Windows] use more precise timing and sleeping

Achieved sleep behaviour is still worse than on Linux, but it's now the
best Windows can do.

Enables sys_usequeryperformancecounter by default. Most modern games use
this. Very old machines or Windows VMs may benefit from disabling it.

Fixes sys_usequeryperformancecounter issue where if enabled at startup,
timer precision was only 15.625ms.

Removes workaround for compilers that don't support 64 bit integers.

Updates documentation.

Signed-off-by: bones_was_here <bones_was_here@xonotic.au>