utility types

WIP

This crate use proc-macro to realize several utility types of TypeScript

Example

source code:

```rust

[partial(PartialArticle)]

[pick(ContentComments, [content, comments], [Debug])]

[omit(AuthorLikedComments, [content], [])]

pub struct Article { author: String, content: String, liked: usize, comments: T, } ```

generated code:

```rust pub struct Article { author: String, content: String, liked: usize, comments: T, } pub struct AuthorLikedComments { author: String, liked: usize, comments: T, }

[derive(Debug)]

pub struct ContentComments { content: String, comments: T, } ```

Known Issue

Currently I don't analyze which generic is used in the generated struct or enum. So rustc will complain if the field with generic is not included in the generated struct or enum.