NR 1.1.3 and Changes update w/ new Clef Appendix

NR 1.1.3 and Changes update w/ new Clef Appendix

Updated changes.tely to show the extra variations on the new Clef glyphs
(i.e. there are 4 separate glyphs but there are different \clef names using
those glyphs but in different positions.

Added a new Appendix to the NR showing all the standard \clef types
(not including 'ancient music' clefs) in a table, illustrating their
names and where middle c sits relative to the clef. Because of this
I have modified 1.1.3 referencing this appendix instead of listing
them all directly in the Clef section. Also added two useful Clef
related snippets that were already created.