Document gauss.simba (partial)
Add: TInventory.MouseSlot
TInventory -> TRSInventory
Inventory.IsVaildSlot -> Inventory.SlotIsVaild

More human readable name per usage, ie
`if Inventory.SlotIsValid(5) then`
vs the old one:
`if Inventory.IsValidSlot(5) then`

You get it? :)
Inventory structuring.. + fix.
shared/gauss.simba -> shared/random.simba

Random "gaussian" values is ... random. And when the point comes where
we want some "none gauss" random functions still need a "random.simba",
so just have it all in "random.simba".