TwelveOclock: add new instant answer to help with 12 am/pm
TwelveOclock: improve friendliness of answers.

- Answer questions "when is noon?" and "when is midnight?"
- Include such questions as secondary_example_queries
- Be less aggressive in the answer with a comma instead of a period

Includes some internal renaming and reorganization, plus comments to
better reflect the purpose of each bit.
TwelveOclock: add answer_type and is_cached.
TwelveOclock: add and style HTML answer.
Merge pull request #640 from mwmiller/threat_level_midnight

TwelveOclock: add new instant answer to help with 12 am/pm