rose documentation: fix syntax highlighting for incorrect ignore use

Currently,
```
foo=A
!    =B
     =C
```

(note: GH messes with the indent)

in a file edited with a Rose syntax highlighting plugin will have the <samp>!</samp> line highlighted as an ignored option, when in fact it is a syntax error for a value.

This makes sure that ignored options always have a non-whitespace, non-<samp>!</samp> character following the one or two <samp>!</samp> ignore characters.

@arjclark, please review.