Add workflow to run build script periodically

[josh-hadley]

Purpose is to catch changes in dependencies and be proactive on toolchain changes. Workflow should:

• run periodically (once a week? month?)
• diff against latest release
• if possible, auto-create issue on failures

[josh-hadley]

WIP:

• Previous runs
• Workflow source
• currently set up to run weekly (Friday evenings Pacific time)
• can also trigger "manually"
• buildFont.sh modified to exit with error if any step fails so that workflow step also fails, alerting to possible problems

TO DO:

• [ ] log environment info (OS version, Python/pip version, pip freeze)
• [ ] diff/log font output against previous release (notify/warn/error if different)