Validates Finnish Personal Identity Code (Finnish: henkilötunnus / HETU).

A code consists of eleven characters of the form DDMMYYCZZZQ, where DDMMYY is the day, month and year of birth, C the century sign, ZZZ the individual number and Q the control character (checksum).

Individual numbers 900–999 are used for temporary personal identification.

iex> FinnishPic.validate("131052-308T")
{:ok, %FinnishPic{
  birth_date: ~D[1952-10-13],
  gender: :female,
  temporary_id: false
}}

iex> FinnishPic.validate("931052-308T")
{:error, :invalid_date}

Implementation only validates the Personal Identity Code and does not tell if it is really used.