Documentation updates
  - Integrate switches-parameters-and-modes changes from fix-the-hierarchy
    into acl2-doc.lisp, in consultation with Matt
  - Move XDOC topic underneath Documentation

Tweak .gitignores

git-svn-id: http://acl2-books.googlecode.com/svn/trunk@2528 303c5b2c-9740-0410-b014-fd8f9db7be32