Apparently the current recommendation is for a smaller threshold when
using the "generic"-style alignment macros (short jumps are cheaper on
newer CPUs.)
Also change the alignment threshold definition to reflect the maximum
number of padding instead of when to start using jumps.
Add a builtin equivalent to the %include directive called %use.
%use includes a standard macro file compiled into the binary; these
come from the macros/ directory in the source code.
The idea here is to be able to provide optional macro packages with
the distribution, without adding complex host filesystem dependencies.
