Fast generics

[arian]

Add implementGenerics method to shell, which is the same as implement, but the methods can be in a generic form, so function(self, arg1, arg2, ...).

Using this form, the common case, where the methods are used as generics, array.each(arr, fn), is optimized, so not wrapped, as it used to be with the implement case.

[jdalton]

I actually had a WIP issue I hadn't submitted yet for improving the common case of generics. This may also be the place to discuss simply switching the default behavior of implement. Other libs like Underscore/Lo-Dash simply call it mixin (adds generic methods to the _ and adds wrapped equivs to the _.prototype).

[kamicane]

Closing, as the old split-generics branch is now in master.