- add instructions class
- add hoop, pulse/mm and zero point in document

- replace the array (curves, stitches, threads,...) by list to be more flexible with delete and moves of elements
- refresh curves only when needed

add thread class (stitch one, not computing) to deal with color, width and later (maybe) rendering style

second move to a MVC design

add a OE_svgParser class to fill the document
first move to a MVC design

subcurve only work if start<end for now