Add a centralized glossary document for the NaCl documentation.

This is to avoid a separate Glossary in many different documents. The quick
start was also updated to refer to it.

BUG=https://code.google.com/p/nativeclient/issues/detail?id=3634
R=binji@chromium.org, mackinlay@google.com

Review URL: https://codereview.chromium.org/23583058

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@224999 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 224999