Issue 4211: Add an alternative quarter rest shaped like a mirrored Z.

Issue 4211: Add an alternative quarter rest shaped like a mirrored Z.

For example, see G. Ricordi's edition of Don Pasquale by G. Donizetti,
Atto Primo, Introduzione, measure 4, bass staff:
http://javanese.imslp.info/files/imglnks/usimg/1/1a/IMSLP141736-PMLP58429-Donizetti_-_Don_Pasquale_VS_Sibley.1802.16329.pdf
Many other quarter rests in the same score look slightly different.

This new rest is designed to fit in with the other rests in the Feta
font rather than to reproduce a particular historical look exactly.