Support Nested lambdas

Support single line nested lambdas:

``` python
a = (x) > (y) > x + y
a(1)(2)
>> 3
```

Support multiline nested lambdas:

``` python
a = (x) > (
    z << (y) > y + x,
    u << (v) > (
        v << v + z(v),
        () > v
    ),
    u (3)()
)

a(2)
>>> 8
```
