Improve and add weapon descriptions

I kinda made a promise some months ago. It’s about time I fulfil it!

This PR improves all the weapon descriptions in the game. This includes:

* Default weapons
* Weapons of `funwithguns.cdogscpn` (descriptions added)

All descriptions also come with a couple of fact sheets, showing infos like:
* Damage
* Cost
* Rate of fire in rounds per minute
* Lifespan in seconds

I hope these little fact sheets make it easier for the weapons to be compared in-game. :-)