Spec typo cleanup

I've updated the spec to fix some minor typos to make it more consistent
with other W3C specs:

   - Table of Contents now has consistent spacing (IDL names are now shown
   verbatim, rather than interspersing additional spaces).
   - "user agent" is now consistently lower-case.
   - The references section had two URIs that were missing the trailing "/"
   suffix.

https://dvcs.w3.org/hg/speech-api/rev/93afe62c5620

If you see any other typos or issues (minor or major), let us know.

As always, the current draft spec is at:
http://dvcs.w3.org/hg/speech-api/raw-file/tip/speechapi.html

/Glen Shires