Support for multiline display bracket-wrapped formulas

This will fail:

```
\[
\begin{aligned}
\text{Class A front-end} &= 0.025 \times 50{,}000 = 1{,}250 \\
\text{Class A 12b-1 (4 yrs)} &= 0.0025 \times 50{,}000 \times 4 = 500 \\
\text{Class A total} &= 1{,}250 + 500 = 1{,}750 \\
\text{Class C 12b-1 (4 yrs)} &= 0.01 \times 50{,}000 \times 4 = 2{,}000
\end{aligned}
\]

This is not a bug, but lack of functionality.