merged Sequence.Ops into Sequence.Sequenceable

Eliminating superfluous "Ops" traits (GitHub issue #14)
merged SequenceOps into Sequenceable, and pulled the latter out of Sequence

Eliminating superfluous "Ops" traits (GitHub issue #14)
pulled Alternative out of Alternation

Eliminating superfluous "Ops" traits (GitHub issue #14)
merged AlternationOps into Alternative

Eliminating superfluous "Ops" traits (GitHub issue #14)