scopefunc - use kotlin-like scope functions

Add trait defining kotlin-like scope functions.

Currently provided functions are:

• transform(): transform value to another.

  let v = gen_rand(0, 10).transform(|v| 'x'.repeat(v));
  // => `v` is random length of "xx...".
  

• modify(): modify the value and return.

  let v = vec![1, 2, 3].modify(|v| v.push(4));
  // => `v` is [1, 2, 3, 4].