Angled arrows

It'd be really great to have support for angled (and even crossing!) arrows, to represent messages being sent e.g. over a network.

Example: http://tex.stackexchange.com/questions/99436/network-message-sequence-diagram

I fully realize this would be nontrivial to add: finding a good way to represent such diagrams in text is a challenge on its own. It'd probably be wise to consider this a 'other diagram' (I don't seem to be able to add milestones to issues though). Hopefully much of the rendering and styling code can be generalized/re-used, though.

Inspiration for the textual representation could be:

• http://satoss.uni.lu/software/mscpackage/
• https://code.google.com/p/msc2svg/wiki/Example
• http://www.mcternan.me.uk/mscgen/

Though none of those are particularly appealing.

search terms: diagonal, slanted