Smarter placement of wire decorations in TikZ wiring diagrams

[epatters]

The TikZ wiring diagrams now look pretty good, with one important exception: the placement of wire decorations (arrowheads, in compact closed categories; labels, in general) is poor. As a result, manual adjustment of the labels is sometimes needed for complex diagrams.

The problem arises because correct placement of wire decorations is not functorial, unlike the rest of rendering algorithm. Rather, decoration placement is a global operation. For example, a composition of identity morphisms should get a single label and/or arrow, not one for each identity in the composition.

[epatters]

The TikZ wiring diagrams have just been rewritten. The problem raised in the second paragraph is no longer relevant, since wires in the wiring diagram now correspond one-to-one with paths in the TikZ picture. However, wire labels have not yet been implemented, so I'll leave this issue open for now.

[epatters]

Superseded by #73.