Make it visually easier to recognize similar sub-patterns

[Boscop]

In many macros, multiple branches share a lot of similar sub-patterns. It would be easier to visually read the diagrams if the similar sub-patterns were aligned. E.g. aligning the 4 occurrences of macro_name ! into one column in this example, and also aligning the 2 occurrences of values = vf ,.

And for macros where a sub-patterns appears verbatim in multiple branches of the macro (or multiple times in one branch), it would make sense to highlight that they are not just similar but the same, by factoring out that sub-pattern into its own sub-rule diagram (and then inserting the name of the sub-rule (or an arrow to the sub-rule diagram) in place of the occurrences of the sub-pattern).

[lukaslueg]

Moved to lukaslueg/railroad#10 since this is generic