clock 0.3.1

• Parsing into a date-time type that is coarser than the original string is now
  considered ambiguous and undefined behavior. For example, parsing a string
  with fractional seconds using date_time_parse(x) or
  naive_time_parse(x, precision = "second") is no longer considered correct.
  Instead, if you only require second precision from such a string, parse the
  full string, with fractional seconds, into a clock type that can handle them,
  then round to seconds using whatever rounding convention is required for your
  use case, such as time_point_floor() (#230).

  For example:

  x <- c("2019-01-01 00:00:59.123", "2019-01-01 00:00:59.556")
  
  x <- naive_time_parse(x, precision = "millisecond")
  x
  #> <time_point<naive><millisecond>[2]>
  #> [1] "2019-01-01 00:00:59.123" "2019-01-01 00:00:59.556"
  
  x <- time_point_round(x, "second")
  x
  #> <time_point<naive><second>[2]>
  #> [1] "2019-01-01 00:00:59" "2019-01-01 00:01:00"
  
  as_date_time(x, "America/New_York")
  #> [1] "2019-01-01 00:00:59 EST" "2019-01-01 00:01:00 EST"
  

• Preemptively updated tests related to upcoming changes in testthat (#236).