Corrected piezo spelling

In the source code, the spelling of piezo has been changed from "pizo"
to the longer but more correct "piezo."

The program has not changed, just the names of some constants,
variables, and functions.
"cfg regn"/"text fmt" is now "cfg regn"/"misc fmt"

I've renamed "cfg regn"/"text fmt" to "cfg regn"/"misc fmt" both in
the menus and the source code.  This completes the last of several
trivial changes on my to-do list.