Refactoring of contrib_comnmentary.retro

commentary.retro

Original by docl:

{{
variable tmp
: nf whitespace dup @ tmp ! off ;
: rf tmp @ whitespace ! ;
---reveal---
: ::: nf 10 accept rf ;
}}

I believe the filtering ("nf", "rf") could be done better.

Given:

variable tmp
: nf whitepsace dup tmp ! off ;
: rf tmp @ whitespace ! ;

Since the stack won't be touched outside of ":::", we can eliminate "tmp" variable:

: nf whitespace dup @ swap off ;
: rf whitespace ! ;

Taking it one step further, both definitions can be merged with "later":

: filter ( - ) whitespace dup @ swap off later whitespace ! ;

And then, adapting ":::" to use it:

: ::: ( "- ) filter 10 accept ;