Packing a great deal of story into a one-hour package, “Pure Evel: American Legend” tells us as much about where we are now as it does daredevil motorcyclist and ‘70s icon Evel Knievel. Huckster, showman and — in the words of a biographer — in the “Hall of Fame for hedonists,” Knievel pioneered a wedding of TV and extreme sports that has become common currency, as well as a flag-waving streak that played perfectly as a counterpoint to Vietnam-era unrest. Both history and a fascinating profile, “Pure Evel” — timed to what would have been Knievel’s 75th birthday — is purely entertaining.