Introduce crit splitting

Developer-Level Errata

```
second release, p. 57, right column:
"Some items, however, may be broken up among multiple sections (and are noted as such on the Weapon and Equipment Tables).
The weapons that may be mounted in multiple locations—the AC/20, Ultra AC/20, LB 20-X AC and the heavy Gauss rifle—must be placed in adjacent body locations, and automatically receive the most restrictive firing arc."
Change to:
"Some items, however, may be broken up among two locations (and are noted as such on the Weapon and Equipment Tables).
Any ranged weapon occupying 8 or more critical slots may be split between any two adjacent locations. If so, it automatically receives the more restrictive firing arc of the two."
```

crit splitting will be implemented using dynamic slots