Salvo size option for weapons and mounts

**What do you want to see?**
A new parameter for weapons and mounts: salvo size. Normally this would be 1, but increasing it would cause a weapon to fire multiple shots at its target every time it is fired. All shots would go to the same target but have independent to-hit rolls. If a shot that's not the last shot in a salvo destroys the target, subsequent shots would still consume supplies as they're considered to be fired simultaneously or in rapid succession. Salvos could be displayed in a special fashion in battle replays (e.g. fired all at once or in rapid succession) to distinguish them from multiple weapons firing and to save time. The regular reload time rules would apply, so if a weapon takes 3 turns to reload and fires 4 times, it would fire 4 shots, wait, wait, fire 4 shots, wait, wait, etc...

**How would it help players?**
This would be a new feature for modders that they could use to add depth to combat. For instance, a quad barrel mount might be smaller and cheaper than a heavy mount, but not as good as piercing emissive/crystalline armor due to the firepower not being concentrated in one shot. If mounts are given the ability to affect reload time (#502), it might also take longer to reload than a single shot, but less than four times as long.

**Alternatives**
Maybe salvos could be split among multiple targets? But that loses some of their uniqueness vs. just installing multiple weapons. Also maybe extra shots after destroying a target could be held instead of wasted to save supplies? But that seems a bit unrealistic for weapons like shotguns and burst-fire autocannons.

**Screenshots and mockups**
N/A

**Things to consider**
Should the mount option for modifying salvo size add/subtract, or multiply/divide? Maybe options for either? Right now I think multiplying would be more balanced since a weapon that already fires 4 times would benefit from doubling that to 8 better than just adding 1 and getting 5 which is almost useless. But that could add some diversity...

Could salvo size be fractional? Like if it's 2.5, then when the weapon fires the first time, it fires twice, and the next time it fires three times, then twice, then three times again... Or the other way around, if it starts fully loaded?

**Related issues**
This option would mesh well with the option to have mounts affect reload rate (#502).