Adds realistic (read: full size, not "fun" size) nuclear weapons.

Includes a 20 ton TNT equivalent nuclear artillery shell. Higher yields to come, but factorio limits projectile ranges to 1000 tiles, so I'll need to use a different method. Be careful with artillery on auto-fire! They do not respect the minimum range of nuclear shells, so they will destroy your base if you're not careful.

Current modeled effects are:

• Damage due to overpressure

Planned modeled effects include:

• Damage due to dynamic pressure (wind)
• Speed of shock front
• Flash
• Prompt radiation
• Fallout
• Cratering