Moved/merged to scheme-using.texi, as REPL features.
(Examples): New.
(Intro to Breakpoints): New introductory text here. Removed all
subnodes except for Breakpoints Overview.
* scheme-using.texi: New.
* guile.texi (Programming in Scheme): Include new
scheme-using.texi file.
* Makefile.am (guile_TEXINFOS): Include new scheme-using.texi
file.