Update: added a couple of utility functions.

keys(dict) - shortcut to Object.keys(dict)
rand_chance(dict) - picks a random key from a dict of odds in 100,
    to be used for, say, deciding what item to produce out of a
    list of items like, {"stone": 80, "bone": 20, "cone": 50}.
    "stone" should come out more frequently than cone and bone.
    (That is what tests.js was written for. But it will also be
    updated with more tests in the future.)
Cleanups for utilities.js and dev-demos/02

Refactored some bits of game.js, which hopefully makes several
functions reusable and shorter to code. Also added a has_key
function in utilities.js so we don't keep typing Object.keys(x)
.indexOf(y) >= 0.

Bugfixes in 02 scripts.
Update: dev-demos/02 provisions for grid occupation by enemies.