update + some questions

[Bobby Powers <bobbypowers@gmail.com>]

Hi folks, I've been going through the spec, and have a few clarifying questions:

1 - required sim specs.  I'm not sure they should be required by the
spec if we want to support modules/includes of vendor-specific unit
files, styles or macros.   This is sort of covered towards the end of
the overall section with the section on format of include files, but
this is a little confusing to me (suggesting files included are not
necessary XMILE files, but some subset).

2 - Model units.  We don't actually specify the syntax of model units
in the overall part, and the example uses the old-style isee syntax of
'x/(b-c)' to workaround the limit of only allowing a single '/'
character.  I don't mind that example, but would not want to limit the
spec to a single division symbol.

I've commited my changes to the overall section, and will work on the
next sections tomorrow.  Thoughts, comments and criticisms welcome!