Initial work on item weight and volume..
Added checking weight of item vs carried weight when picking up
Added display of weight/volume in character menu, added backpack item, and added volume and storage space to relevant items in items.cfg
Added checks for added/removed storage space on pickup/drop.. doesn't account for non-equippable items, ie: multiple backpacks, but it's almost there..
Renamed weight/volume functions and related calls
Shuffled around player.max_load to weight_capacity()
Derped and forgot to give weight_capacity() a return
Added check for if equipment is actually equipped before adding weight/volume capacity bonuses
Added menu for pick_up when there are multiple items in a tile
Moved weight/volume display to inventory and made one minor bugfix
Added check for empty equipment slot to skip vol check on pick_up
Merge pull request #79 from KittyTristy/weightvolume

[WIP] Support for item weight and volume, storage space