Equipping weapons, and inventory item stacks

* Melee combat with default damage from all items and specific damage
from weapons designed for battle.
* Items are stored in stacks in the inventory now because all objects
now have __eq__ method (by comparing __dict__ values).
* Tests for player inventory and equipment.
* Add a knife.

Commit references #18.
Messages for melee brawl

* Remove __eq__ from all objects except for items (unnecessary).

Commit references #18.
Add equip command for client

* Hit "e" to equip an item, hands only for now. Item needs to be in the
inventory.

Commit references #18.
Add ability to drop items

* Hit "d" and type in an item name to drop an item.

Commit references #18.
Allow unequippping of items

* Hit "u" and type in a slot name to unequip an item in this slot.

Commit references #18.
Items can be equipped in different slots

* Equip command takes two comma-separated arguments: "item, slot", where
default slot is hands.

Commit references #18.
Player can view equipment

* Hit "E" to view equipment.

Commit references #18.
Merge branch 'equipment' into develop

Commit closes #18.