Unify siege armor. Buff bolt shooters and siege towers slightly. Reviewed by fatherbushido.

Increase crush armor of most siege from 1 to 5,
decrease crush armor of rams from 10 to 5.

Bolt shooters were not affected by r18037, but nerfed too much in r16392.
Thus make them stronger as in that commit, but weaker than before it by
increasing their repeat rate by 25%.

Remove minimum attack distance of the macedonian siege tower and
shoot one arrow per unit garrisoned but at most 10 arrows,
rather than shooting only one arrow for 2 units garrisoned.