Move the documentation of the target configuration form to
Configurations/README.

Move initial assembler object templates to
Configurations/00-BASE-templates.conf.

Furthermore, remove all variables containing the names of the
non-assembler object files and make a BASE template of them instead.
The  values from this templates are used as defaults as is.  The
remaining manipulation of data when assembler modules are used is done
only when $no_asm is false.

While doing this, clean out some other related variables that aren't
used anywhere.

Also, we had to move the resolution of the chosen target a bit, or the
function 'asm' would never catch a true $no_asm...  this hasn't
mattered before we've moved it all to the BASE template, but now it
does.

At the same time, add the default for the 'unistd' key to the BASE
template.

Reviewed-by: Rich Salz <rsalz@openssl.org>