* chore(highland): add Alvis Tang as an author
* fix(highland): correct the definition of push
A push function should have a type of
```ts
(err: Error | null, x?: R | Highland.Nil) => void
```
such that it can accept
```ts
push(null, _nil);
```
to signal the end of the stream.
* fix(highland): add the missing defintion of uniq and uniqBy
See http://highlandjs.org/#uniq
* fix(highland): correct the definition of each
As a special case, `done` is allowed to attach to the stream after `each`.
See http://highlandjs.org/#each
* fix(highland): correct the definition of merge
The merge function should not take any argument. Also the return of a merged
stream should be the union type of the origins.
See http://highlandjs.org/#merge
* fix(highland): add the missing definition of toPromise.
See http://highlandjs.org/#toPromise
Andy Hanson