Add EntityKnockback (Arrow) property

A property for arrow knockback power
Add a lead argument to shoot

An experimental new aiming system, works nicely so far...
Add tag server.get_npcs_flagged

A fairly useful self-explanatory tag
More minor fixes and patches

- fix bad regex in entity spawns, clean meta, add identifySimple's
- fix meta
- handle mobprox flags faster (before respawn)
- allow the 'matches' comparison in the is[].to[] tag
- throw less errors in entity.can_see
- run dList.formatted faster (don't do full comparisons, just check the
object identifier)
- find.entities better