Fix Rocket artillery

Rockets were high-intensity "shock and awe" barrages but suffered these drawbacks when compared to conventional artillery:

• Long-reload times to prepare multiple barrels for next fast barrage
• Time to move and redeploy because the rocket trails invited fast destruction from the enemy's counter-battery fire

Low ammo supply simulates both long reload time and time to redeploy within a hex.

The trade-off is high SA/HA for low ammo.

Possible New Rocket Units (besides the obvious nebelwerfers and katyushas:

• US Sherman Calliope
• US Screaming Mimi "towed" (transported) rockets
• British Land Matress towed rockets
• British/US LCT(R) close-support landing craft