Create setup.py

installs ly2video.py, midi-rubato, xsc2beatmap to /usr/bin (or /usr/local/bin, or whatever)
and everything in ly/ folder as a python module.
Added directions to install properly
Merge pull request #51 from luolimao/master

Add setup.py for easy installation
Added specific install directions for Arch Linux
Merge pull request #53 from luolimao/master

Added directions for installing on Arch Linux
remove trailing whitespace
make it clearer that \midi is required
remove unused previewFiles variable
remove unused previewFilesTmp variable
improve error-checking in generation of preview .png
use "command" not "directive"
allow easy copy'n'paste of lilypond command
add helpful suggestions about needing \layout { }
add comment explaining why -dmidi-extension=midi is required
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