* Initial implementation adding tz recipe as a dependency
* Apply patch from PR date#611 to add ability to specify tz database by
  environment variable and also enable the binary tz database to be
  parsed on windows
* Deprecate use_system_tz_db in favour of "with_tzdb" option to handle
  all mutually exclusive options
* Add with_db_format option to provide flexibility in how the tz recipe
  is consumed

* Add patches for v3.0.0 and v2.4.1 that hotfix the changes present in
  HowardHinnant/date#611 on to these older versions. This will allow all
  versions of date currently on CCI to utilise the tz package as a data
  source for the timezone database.

  Some additional modification of the build system was required in these
  patches to ensure a consistent interface across versions. Only the
  minimal changes necessary to introduce desired features were made,
  preserving deficiencies associated with older versions of date.

* Fix issue in existing patch in which a string to replace '/' with '\\'
  in windows paths was attempting to operate on either a string_view or
  a const string, which was causing compilation errors. This was
  rectified by making a copy of the string before modification.