Update on the Guile bindings

[Ludovic Courtès]

Hello!

I’ve merged the (gnutls) and (gnutls extra) modules in ‘master’ to
reflect recent changes in that area, and updated the doc accordingly.

While I was at it I’ve changed the installation path of the loadable
Guile module: formerly it was installed as
$libdir/libguile-gnutls-v-1.la, and now it will be installed as
$libdir/guile/X.Y/guile-gnutls-v-2.la, where X.Y is the effective
version of Guile (currently 1.8 or 2.0).

The previous path was inappropriate since this shared library is not
meant to be used from C.  (In fact, this change had been requested to me
looong ago when guile-gnutls was first packaged in Debian.)

Thanks,
Ludo’.