Compound assignment for PIPE, COPY and COPY ALL?

I experimented a little with the compiler for fun and added compound assignment for `|>`, `<<<` and `<<<<`.

However, since it is so easy to implement, I suspect there's a reason it has not been done already. Is there maybe a better way to achieve `x = x |> f` without repeating yourself? Or does it break functionality in some subtle way?

***

Examples:
```
list = [1 to 6]
list |>= reject odd
console.log list #=> [ 2, 4, 6 ]
```
```
obj = a:\a
obj <<<= b:\b, c:\c
console.log obj #=> { a: 'a', b: 'b', c: 'c' }
```