* doc/ref/libguile-parallel.texi: New file, documenting parallel
installation and the use of pkg-config.
* doc/ref/libguile-linking.texi: Adapt.
* doc/ref/libguile-autoconf.texi: Rename from autoconf.texi. Lower
sections, and integrate in the "Programming in C" chapter.
* doc/ref/guile.texi: Adapt.
