Note: not ordered. do whatever I/you want

+ Check GB03, again
+ Hacky text printing, typewriter-like, with PF2 font
  ok I won't forget frontend, but it's different
+ Better CLI, e.g. invoke imagemagick if input is not PBM
+ Consider better MTU adaption
+ Consider better BLE traffic regulation, with BLE notification
+ Consider the printer 'text' mode, it can make things faster
+ Consider more control to something like 'energy'
+ Consider keeping server backend (more) secure to be used by IPP
+ Clean up CUPS/IPP code
+ Make a build guide for android:
  Summary the hacks to p4a, bleak p4a recipe, p4a webview bootstrap, and AdvancedWebView
+ More frontend usability, more functions
+ A better layout for mobile?
+ Better Canvas mode, (re-)consider fabric.js
+ Implement Document mode, (re-)consider html2canvas.js
+ Write good help/manual
+ Make error notice short while let users see detailed help/manual for what-to-do
+ ...

? Compression for GB03 data
? Put Android APP on F-Droid? But it needs automatic build system...
  Android guys can help this!