miniboosts 0.4.0

MiniBoosts: A collection of boosting algorithms written in Rust 🦀
Documentation
# CHECK LIST
This is a check list before updating `MiniBoosts.`


## Version numbers
Update the followings:

- [_] `Cargo.toml`
- [_] `README.md`
- [_] `src/booster/`
    - [_] `lpboost/`
    - [_] `erlpboost/`
    - [_] `mlpboost/`
    - [_] `softboost/`

## Update TAG (GitHub)
```bash
$ git tag [tag name]
$ git push origin [tag name]
```