Added a replace() proc using a callback to pegs.
Added a replace() proc using a callback to pegs.

I was missing a nice way to use pegs with a more specialized replace
functionality. Here my try to create a universal and versatile version
of replace for that.

singularperturbation/Nim,dom96/Nim,zachaysan/Nim,jfhg/Nim,haiodo/Nim,russpowers/Nim,dom96/Nim,mbaulch/Nim,zachaysan/Nim,jfhg/Nim,zachaysan/Nim,tulayang/Nim,russpowers/Nim,zachaysan/Nim,singularperturbation/Nim,mbaulch/Nim,haiodo/Nim,mbaulch/Nim,russpowers/Nim,dom96/Nim,haiodo/Nim,singularperturbation/Nim,mbaulch/Nim,mbaulch/Nim,jfhg/Nim,dom96/Nim,tulayang/Nim,singularperturbation/Nim,russpowers/Nim,tulayang/Nim,haiodo/Nim,russpowers/Nim,zachaysan/Nim,zachaysan/Nim,tulayang/Nim,haiodo/Nim,jfhg/Nim,russpowers/Nim,singularperturbation/Nim,jfhg/Nim,tulayang/Nim,jfhg/Nim,haiodo/Nim,haiodo/Nim,singularperturbation/Nim,tulayang/Nim,dom96/Nim,jfhg/Nim,mbaulch/Nim,dom96/Nim,dom96/Nim,mbaulch/Nim,russpowers/Nim,singularperturbation/Nim,zachaysan/Nim