Allow relation symbols with parameters

Parameters must follow the relation symbol and be surrounded by braces, like so: `\rel{x}{y}{z}`.

This attempt is still brittle/broken in a few ways:
- It makes using braces in creative ways in mixfix notation ambiguous.
- It does not verify that the parameters are used in a consistent manner for each symbol. It essentially allows users to define  `a\MyRel b` and `a\MyRel{x} b` (and ones with even more parameters).
- It allows parameters for all relation symbols, even for those where it makes no sense in ordinary TeX markup, e.g. `a <{x} b`.

0 files changed, 0 insertions, 0 deletions