Improvements to spoken ATIS

Improvements to spoken ATIS

- Add section tag to support inclusion of ATIS fragments.

- Add visibility, QNH and cloud tokens to support new ATIS formats.

- Add support for starts-with, ends-with and contains comparisons in
  conditionals, including negated versions.

- Strip and convert case in comparisons.

- Speak VRB wind direction as "variable".

- Speak zeroes in fractional part of QNH inHg.

- Force US voice in US, Canada and Pacific; UK voice in UK.