further improve output of shell commands
fix bug handling set-global-staff-size and \bookOutputName

Any line after the one mentioning set-global-staff-size or
\bookOutputName was incorrectly getting eaten.
add debug to removal of \paper section
remove -same_quant (fixes #44)

Fixes https://github.com/aspiers/ly2video/issues/44
refactor creation of title frames from static image
prepare for allowing generation of multiple silent audio tracks
add --padding option