TODO

PyFeyn TODO
-----------

 * Use the property() descriptor to bind foo.x to foo.get/setX() appropriately.

 * Write a manual.

 * Transparently pass single options and lists of them using isinstance(foo,
   list).

 * Add defaults mechanism for 3Dness, thicknesses, colours, fancy bosons...

 * Introduce unit testing

 * setStrokeStyle(color=None, thickness=None, trans=None, others=None) etc. -
   hide PyX options.

 * Improve multi-lines. Should be defined by number of lines and
   max-width/half-width OR number and separation. Arrows shouldn't necessarily
   be duplicated on all lines. Auto-sizing to blobs?  Should definitely crop to
   a visible path on the markers/blobs - should the visible path cropper be
   broken out as a standalone internal function?

 * Fix pattern stroke colour problem.

 * Allow setting initial/final straight components of decorated lines.

 * Allow single lines to be deviated sharply (split?) round a vertex.

 * Every diagram element should know its parent diagram.

 * Allow multiple diagrams in a single output image (add a Page class or
   similar).

 * Do hatched patterns better than PyX (or fix PyX's implementation).

 * Improve the global options / defaults mechanism.

 * Allow tree-level diagrams to be generated automatically by minimising the
   "energy" of a specified graph topology (a la FeynMF).