Adding _.method

As proposed in issue #1345 here's a pull request for _.method, i.e. method function support,

This is quite concise when executing the same function on a collection of objects (varying context), e.g.

_.any(views, _.method("isDisabled"));

In addition, _.method supports currying, e.g.

_.method(foo, 3)

will create a member function that calls foo with 3 as the first argument.