Rename uuid package to random. No further changes.
Rename Meteor.id() -> Random.id()
Get rid of duplicate random code inside minimongo.

Temporarily move the objectid-specific function into random.js.
Use Random.id() in Spark.

We couldn't use Meteor.uuid() because it contained '-' but Random.id() is fine.
Replace almost all uses of Meteor.uuid with Random.id.
Meteor.random -> Random.fraction
add Random.choice
move objectid generation back into objectid class
Move Meteor.uuid to past package. Add Random.hexString.
Document random package.
Move random generation code from minimongo and uuid packages to new random
package.

The new API is Random.id(), Random.fraction(), Random.choice(arrayOrString), and
Random.hexString(digits).

Meteor.uuid is kept around for backwards compatibility.