• http://infiniteundo.com/post/25326999628/falsehoods-programmers-believe-about-time
• http://infiniteundo.com/post/25509354022/more-falsehoods-programmers-believe-about-time
• http://rachelbythebay.com/w/2017/09/27/2153/

function date_parse {
  if date --utc >/dev/null 2>&1; then
    # GNU/date
    date -u --date "${1}" "+%s"
  else
    # BSD/date
    date -j -u -f "%F %T" "${1}" "+%s"
  fi
}