Enumeration of java.io.InputStream in bytes.

Refactored and generalized the existing enumReader function to
produce a similar enumInputStream function.
fix NumericPLens
Merge pull request #404 from xuwei-k/request/numeric-plens

fix NumericPLens
Enumerator for java.io.InputStream
Merge pull request #366
fix IterateeT scaladoc
fix StepT scaladoc
cleanup StreamT instances

1. remove `StreamTMonad`. it is unnecessary because `StreamTMonad` and `StreamTMonadPlus` requires same typeclass. (like ListT)
2. relaxed `StreamTMonadPlus` constraint
add StreamT tests
Merge pull request #406 from xuwei-k/cleanup-streamT

cleanup StreamT instances
Typo in applicative identity test.