Various setlist enhancements

[ptsefton]

• Allow comments in setlist, added to the top of each song, eg "Go fast!" or "Start with bass"
• Produce printable tear-out setlists in a big font including the comments
• Show keys in setlist output
• Allow transposition in setlist using {transpose: } directive (and while we're at it, change books so they work the same way)

[ptsefton]

I think the best way to implement setlists is to make them markdown - yes this means that # will be handled differently in songs (Where it is a comment) and in setlists but it will make setlists much more flexible.

{title: North Pole gig 2015-12-25}
# Set 1
## Rudolph
He gets cranky unless we play this, so make sure he's listening
## Another song

# Set 2
## Rudolph {transpose: +1}
### Play loud!

## Rudolph {transpose: +2}
Three times might not be enough, consider doing it again for encore

...