assign 'let()' or other accessor value as a subject

Created by: moro

Hi, thanks to nice testing framework.I use rspec every day.

I have a small feature request. This patch extend subject() to use accessor return value (especially defined by let() ).

I know that's already usable by writing :

let(:var) { "some value" }
subject { var }

additional syntax by the patch:

let(:var) { "some value" }
subject :var

This helps to express 'I use let value as a subject' more clealy, does'nt it?