Piecewise curly brace

[asavoy]

We need to support expressions like this:

From: https://trello.com/c/VrzOBiI2/8582-piecewise-curly-brace

[stufflebear]

There's a couple conventions for the separator between the two columns (the ":" in your example). I've also seen an only whitespace separator (where the columns line up), a comma after the first column, and an if at the beginning of the second column. We're thinking that it makes the most sense for MathQuill to default to only whitespace with column alignment for the separator. People could type in an additional separator if they desire at the end of the first column or at the beginning of the second column. Is this consistent with what you're envisioning?