HUG songbook

This merge does a number of things, all in the service of getting a songbook for HUG that is both printable and comfortable for the screen.

First, I hacked up the Makefile to generate A4 landscape.  I had been dialing in screen proportions to match the particular display at the Stonemason's Arms, but people seem to really benefit from printing things out on A4.  So I compromised and reformatted things for landscape A4.

I tinkered with a few of the songs in the main directory, but I also added a bunch from the original HUG songbook.

I also toyed with the style a little to make subtle use of colour.  I'm not wedded to the particular colours, but I think the saturation levels should be relatively low to avoid playing hell with colourblindness and with coloured lighting at venues.

Finally, I made chordlab a submodule of this, and aimed the Makefile at that copy, just because that's more comfortable to me.