simmer 3.6.5

New features:

• set_attribute() (and set_global() by extension) can set multiple attributes at once by providing vectors of keys and values (or functions returning such keys and/or values). get_attribute() (and get_global() by extension) can retrieve multiple keys (#122).
• New stepn() method deprecates onestep() (e452975).

Minor changes and fixes:

• Restore ostream after formatting (9ff11f8).
• Fix arrival cloning to copy attributes over to the clone (#118).
• Fix self-induced preemption through set_capacity() (#125).
• Update "Queueing Systems" vignette (a0409a0, 8f03f4f).
• Update "Advanced Trajectory Usage" vignette (4501927).
• Fix print methods to return the object invisibly (#128).
• New "Dining Philosophers Problem" vignette (ff6137e).