Add more weapons and armor

* Create base classes Armor, RangedWeapon and MeleeWeapon.
* Actual items: PowerArmor, Knife, LaserGun, TaserGun.
* Fix tests broken by this changeset.

Commit references #40.
Way to load objects with duplicate chars

* Items with duplicate characters can be loaded by using
dat/maps/*_extras.txt files.

Commit closes #40.
Merge branch 'more-objects' into develop