Don't speak nested brackets as intervals

[NSoiffer]

$[ A , [ B , C ] ]$ is spoken as a nested interval which doesn't make sense. As mentioned in #328, this could be a commutators so the interval speech is particularly confusing.

An obvious fix here is to rule out the interval speech if the bracketed expression is contained inside other brackets. It would be good to try and restrict it as much as possible to only sensible intervals. Anyone with suggestions?

[lnelson2382]

Most instances of interval notation that I have seen have only plain numbers, infinity, and single-letter variable names or their negatives as the ends of the interval. More complicated expressions are probably used in some places, but even in those cases the current method of reading out both endpoints twice is cumbersome and hard to follow.

[NSoiffer]

The ClearSpeak "standard" (not really a standard, but a set of rules defined by ETS) says what it should speak for intervals, so I don't want to change them. I am willing to shorten them when you set SpeechVerbosity=Terse. Ideally it should be a shortened version of the more verbose speech, but I'm not sure what one would use for ClearSpeak. SimpleSpeak uses wording like "the open interval from a to b" which is more terse, but using that for terse mode in ClearSpeak would be very different speech.

@lnelson2382: do you have some suggested speech?