Introduce new operators intended for use by parser combinator libraries.

The expected definitions (which are by no means required) in
parser combinator speak are:

* `p  ~>> f`   =  `bind(p, f)`
* `p1 ~>  p2`  =  `pair_right(p1, p2)`
* `p1 <~  p2`  =  `pair_left(p1, p2)`
* `p1 <~> p2`  =  `pair_both(p1, p2)`
* `p  |~> f`   =  `map(p, f)`
* `1p <|> p2`  =  `either(p1, p2)`
Merge pull request #2702 from alexrp/master

Introduce new operators intended for use by parser combinator libraries.
Revert "Merge pull request #2702 from alexrp/master"

<~ is already a valid expression in Elixir.

This reverts commit 2c741ec6ae8e587322f2148cf2a3c99555bdee57, reversing
changes made to 12a457829feadfe5d4431963753749cb089a3676.
Add free operators

<<~, ~>>, <~, ~>, <~>, <|>
Release v1.0.0-rc2
Start v1.0.0
Remove deprecated code
Properly document Task.Supervisor options