Add error handling for all stream methods that take a function.

Partly solves #94.
Make #zip push errors on the error channel.
Call test.equal in the right order.
README.md: Document where `_` comes from
Add Stream.doto for performing side effects on stream thunks
Fixed typo
Merge pull request #105 from jamesrom/patch-1

Fixed typo
Merge pull request #99 from felixrabe/patch-1

README.md: Document where `_` comes from
Merge pull request #98 from vqvu/zip-push-error

Make #zip push errors on the error channel.
Merge pull request #102 from glenjamin/doto

Add Stream.doto for performing side effects on stream thunks
Merge pull request #97 from vqvu/catch-buggy-fn

Add error handling for all stream methods that take a function.