Adding macros `prog1' and `prog2' similar to cl

This commit adds the macros `prog1'(or do1)  & `prog2'(do2):

`prog1' executes the body sequentially (possibly for side effects),
returning the value of the first expr
eg:
	=> (prog1 (+ 2 2) (print "some side-effects"))
	   "some side-effects"
	   4

`prog2' is similiar to prog1 except that it returns the value of the
second expr