layout.py: bugfixes

layout,song: add more layout options

layout,song: Export more info, add ruby_expand layout option

song,layout: support specifying some layout options in the style

layout: fix boundary condition bug

song: Support merging with combining characters to the left

steptool: add undo and seeking

renderer/glex: fix wrong attribute type

docs: add wrapper script for screen mirroring prior to running blitzloop

Add reference to the blitzloop-songs repo

mpvplayer: fix seeking when a static image is used as video

mpv-visualizer: pass in vo/ao pads as substitutions

docs/songfiles.md: Add examples for making audio tracks

Remove references to ffms/record.py

steptool: initialize volumes