UEB capitalization needs work

Test case `braille::UEB::iceb::hat_12_1_7` is: $A\hat{B}C$.

The output uses a cap word indicator but the example doesn't. This is likely because the last part of the definition in section GTM 12 says "the item is simply the previous individual symbol". Symbol in this case includes the cap indicator. So it seems in this case, $\hat{B}$ should not be considered a cap letter.

The code in `braille.rs` that builds a cap word from caps needs modification to handle "symbols".