QR code displaying - Githubissues

In support of #14 and #1

[x] Generate QR code png using pure python
[x] Use ERROR_CORRECT_L (About 7% or less errors can be corrected)
[ ] Hook up to #5 API and generate QR from invoice request (convert to uppercase)
[x] Resize png using pure python (keep QR centered on white background)
[ ] Add text to top and bottom (e.g. amount to pay, "Scan to pay")
[x] Display generated png on e-ink
[x] Consider writing bitmap to display framebuffer instead of using png intermediate step

lncm / ideas