1.  Cutting "How Learning Works" material from index to instructors' guide.
2.  Putting link to instructors' guide on site home page.
Adding notes to teaching guide
Fix links to glossary

This commit only cover the changes done by

    $ for i in $(grep -lr -e "(../gloss.html" ./novice); do sed -i 's/\.\.\/gloss\.html/\.\.\/\.\.\/gloss\.html/' $i; done
    $ for i in $(grep -lr -e "(../gloss.html" ./intermediate); do sed -i 's/\.\.\/gloss\.html/\.\.\/\.\.\/gloss\.html/' $i; done

Close #393.
Merge pull request #394 from r-gaia-cs/fix-gloss-links

Fix links to glossary
Merge branch 'master' into making-teaching-instructions-more-accessible
Merge pull request #397 from gvwilson/master

Master