lutz v0.3.0 - CRAN release

• V8-based 'fast' method was ported to use Rcpp - it is now even faster, and
  we can drop the V8 dependency. Thanks @hrbrmstr! (#4)
• Bob Rudis (@hrbrmstr) added as an author
• Upgraded time zone map to 2019b
• Dealt with areas with overlapping time zones (#2)
• Added three new functions:
  • tz_list() lists all time zones and information about UTC offsets and daylight savings
  • tz_offset() lists information about a specific time in a specific time zone
  • tz_plot() plots a time zone and its UTC offset for a year, including periods
    of daylight savings.