[CM] Snd 10.8

[Bill Schottstaedt]

> a macro get processed (expanded) when the   
> lambda that contains it gets READ by s7

I think I can implement this, but it will mean that if the macro is
not defined at read time, it will be expanded at eval time.  I looked
at the macro chapter in cLtL2 but they leave these things up to
the implementation; "an implementation...has great latitude in
deciding when to expand macros".  Currently in s7, the quasiquote
expression is expanded at macro definition time, but the macro call
is expanded when it is evaluated.  I think handling it instead
in the reader is easier than splicing its result into the caller 
at eval time (not sure how much this will slow down the reader).