ignore more Vim files
spire binding: convert back and forth between spire's and scalaz' monoids
test conversion spire → scalaz
renamings, remove boilerplate
spire binding: convert back and forth between rings

To be specific, convert between spire's `Semiring` and `Rig` and pairs of
scalaz' `Semigroup` and `Monoid`.
add conversions for AdditiveX, and hence improve tests
spire examples in README
Merge branch 'topic/spire'