______
To-do:



- real undo/redo support
- higher resolution for main data, to make zoom useful.

- other shapes:
  - circle
  - line
  - text


_______________
Partially done:
- use real XML reader: 
        expat is too big (prescribble binary get 100% bigger)
- zoom: experimental zoom working
- gzip read/write support
- faster erase
