Convert a key and value to an iCal line:

iex> ICalendar.Util.KV.build("foo", "bar")
"foo:bar\n"

Don't add empty values:

iex> ICalendar.Util.KV.build("foo", nil)
""

DateTime values will add timezones:

iex> date =
...>   {{2015, 12, 24}, {8, 30, 0}}
...>   |> Timex.to_datetime("America/Chicago")
...> ICalendar.Util.KV.build("foo", date)
"foo;TZID=America/Chicago:20151224T083000\n"

Attendees get their own line, each:

  iex> attendees = [
  ...>   %{"PARTSTAT" => "ACCEPTED", "CN" => "eric@clockk.com", original_value: "mailto:eric@clockk.com"},
  ...>   %{"PARTSTAT" => "ACCEPTED", "CN" => "paul@clockk.com", original_value: "mailto:paul@clockk.com"},
  ...>   %{"PARTSTAT" => "ACCEPTED", "CN" => "James SM", original_value: "mailto:james@clockk.com"},
  ...> ]
  iex> ICalendar.Util.KV.build("ATTENDEES", attendees)
  "ATTENDEE;CN=eric@clockk.com;PARTSTAT=ACCEPTED:mailto:eric@clockk.com\n" <>
    "ATTENDEE;CN=paul@clockk.com;PARTSTAT=ACCEPTED:mailto:paul@clockk.com\n" <>
    "ATTENDEE;CN=James SM;PARTSTAT=ACCEPTED:mailto:james@clockk.com\n"