Exclude spack.__all__ from documentation.
Exclude spack.__all__ from documentation.

Everything in the __all__ list in the spack module is from some other
module, so only do their documentation in their original location.  This
also avoids issues like the fact that some directive names shadow spack
core module names.

krafczyk/spack,EmreAtes/spack,lgarren/spack,iulian787/spack,lgarren/spack,iulian787/spack,mfherbst/spack,LLNL/spack,EmreAtes/spack,iulian787/spack,skosukhin/spack,matthiasdiener/spack,matthiasdiener/spack,lgarren/spack,tmerrick1/spack,EmreAtes/spack,krafczyk/spack,TheTimmy/spack,matthiasdiener/spack,LLNL/spack,iulian787/spack,LLNL/spack,matthiasdiener/spack,EmreAtes/spack,skosukhin/spack,iulian787/spack,mfherbst/spack,krafczyk/spack,lgarren/spack,krafczyk/spack,skosukhin/spack,tmerrick1/spack,matthiasdiener/spack,LLNL/spack,tmerrick1/spack,TheTimmy/spack,skosukhin/spack,mfherbst/spack,tmerrick1/spack,mfherbst/spack,TheTimmy/spack,LLNL/spack,tmerrick1/spack,TheTimmy/spack,EmreAtes/spack,skosukhin/spack,lgarren/spack,mfherbst/spack,krafczyk/spack,TheTimmy/spack