Add timezone metadata from upstream r616
Make internals of buildprefixdata more generic
Merge metadata changes from upstream r618
Generated Python files for metadata
Merge upstream code changes from r618.

Rename carrier.description_for_* to carrier.name_for_*.
Add carrier.safe_display_name().
Add is_mobile_number_portable_region().
Add support for flat (not per-locale) prefix data, and for multiple values.
Generate Python files for timezone metadata
Add timezone mapping functionality as per upstream r616
Add tzdata subpackage to setup
Make doctest robust to 2to3 conversion