where
invoke
groupBy
first
rest
flatten
uniq
add aliases

cc @jonahkagan not tested...not sure the best way to test it.
Could duplicate all existing tests and run them under aliases, but that
seems like overkill.
readme: document how to pass in builtin stream options

cc @jonahkagan @azylman I've been sneaking this feature in as I convert
things for 1.0, but all of the
mixins in the 1.0 branch default to adopting the objectMode of their
upstream, e.g. the stream returned by `_s.each(readable, fn)` will have
the same objectMode as `readable`. I've documented this in this commit,
let me know what you think.

I'd also like to add some sugar to the objectMode option so that you can
specify both the readable and writable side's objectMode:

```
_s.(readable).map(fn, { objectMode: {readable: false, writable: true} })
```

This would let you safely have streams that convert streams of binary/string
data into individual objects and vice versa.
test: add gates on broken tests in < v0.10.20

cc @azylman I think this should fix travis. To be super user-friendly
I'm thinking we should also gate the features themselves, e.g. throw if
a user uses first/reduce/rest and their node version is bad.