Features from optional dependencies

rand implicit feature

Enables rand ^0.3

rand:

Random number generators and other randomness functionality

Affects set::HashSet, map::HashMap, map::RandomState, map::DefaultHasher, set::HashSet, map::HashMap, map::RandomState, map::DefaultHasher, set::HashSet, map::HashMap, map::RandomState, map::DefaultHasher, map::RandomState, map::DefaultHasher, map::RandomState, map::RandomState