Suggest best clef for pitches determined by the least number of leger lines required to notate all pitches on a single staff.
abjad> pitches = [Pitch(x) for x in (-30, 10, 20)]
abjad> pitchtools.suggest_clef(pitches)
Clef('bass')
abjad> pitches = [Pitch(x) for x in (-5, 30)]
abjad> pitchtools.suggest_clef(pitches)
Clef('treble')