add FingerTree, Finger, Node, foldable law test
Classify Codensity.
Instances & lawfulness/implicit resolution tests for Codensity.
Add cobind to Ephemeral stream & check laws.
Merge pull request #530 from S11001001/topic/codensity-instances

Instances & tests for Codensity
override streamInstance#foldMap

it should work if stream is infinite
infinite stream foldRight & foldMap test
Handle foldMap of infinite streams; test. (#531)
Merge pull request #517 from possiblywrong/scalaz-seven

Add cobind to EphemeralStream & check laws.
fix EphemeralStream#tails
EphemeralStream inits & tails test
use cons instead of ##::