a few modifications to the model and additonal links in readme

at this stage its become clear this design is not optimal. moving the Y+Z around at speeds of 300mm/s when it weighs 3kg+ seems excessive.
massive massive rewrite of the main balaur scad file

lots of code refactoring into seperate scad files; suitcase is now
briefcase; L bracket, hinge in their own files.

rethink of the design, especially the Y axis. moving away from tslot
towards smooth rod+threaded rod a la prusa i3. a bracing structure made
of aluminium will contain Z and Y axis and will fold down as previously
thought. the carriages will have to be intricate designs.

the bed will now move beyond the edges of the briefcase to allow for a
usefully high Z (that can fold down). this has raised it to a ridiculous
height; the x carriage will need a lot of thought. the intention is to hide
the electronics down there