Labello: a simple label encoder

This crate provides a simple API for encoding labels represented by vectors. It uses a hashmap as internal data structure for classes and their mapping.

Example

```rust

// load data in a vector let data: Vec = vec!["hello".tostring(), "world".tostring(), "world".tostring(), "world".tostring(), "world".tostring(), "again".tostring(), "hello".tostring(), "again".tostring(), "goodbye".to_string()]; // declare a label encoder let enc = Encoder::new(None);

// fit encoder with ordinal type (default) let enc = enc.fit(&data);

// transform original data to internal encoded representation let trans_data = enc.transform(&data);

// inverse transform internal encoded representation to original data let recondata = enc.inversetransform(&trans_data);

// get unique original elements let uniques = enc.uniques();

```