CCTZ v2.0

[Greg Miller]

CCTZ v2.0 is now available as a release and at head on master: https://github.com/google/cctz. The big changes in this version are:

• A complete civil-time library for computing with human-scale time, such as dates. See the README.md for more background here.
• A time-zone library that converts between CCTZ's civil-time library and the standard <chrono> library.
• The spelling of the API points was changed to a more standard snake case style with lowercase letters and underscores.

We also have more info about migrating from the V1 interface to V2.

Thanks.

Greg