Make `multinomial` work for iterable input

[thchr]

There's no need to restrict the signature to multi-argument inputs; iterable inputs are arguably more natural. This way, we can avoid splatting if the input is an iterable.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 96.89%. Comparing base (912d506) to head (a67609a).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #170   +/-   ##
=======================================
  Coverage   96.89%   96.89%           
=======================================
  Files           8        7    -1     
  Lines         804      804           
=======================================
  Hits          779      779           
  Misses         25       25           

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.