Doc stuff.
Renamed s..list -> s..set again.
Added s.index, and s.indexOf.
Added s..eid.
Made s..eid accessible.
Added comment for s.some.
Not really sure why this had Windows line endings when I've done 100% of it in Unix...
Made docs hide private methods.
Preliminary API docs.
Started trying to figure out ways to denote overloaded arguments.
Made s.size into a property (with a getter) instead of a function.
Added s.id to s.toString.
Made emptyset return ∅ on s.toString.
Started to implement sets as a custom Set object.
Revamped utilities.extend.

Based on http://www.2ality.com/2011/12/subtyping-builtins.html
Exposed S.Set, and started trying to work with s.sort.
A better subtyping of Array.

Based on http://www.2ality.com/2011/12/subtyping-builtins.html and http://www.2ality.com/2013/03/subclassing-builtins-es6.html
Added constructor function to Set.
Got Set working!
s.size now calls s..set.size.