htmlentity
html entity encode and decode.

How to use
```rust
use htmlentity::entity::*;
let html = "
";
let htmlencoded: Vec = encode(html, Entities::SpecialChars, EncodeType::Named);
asserteq!(html_encoded.iter().collect::(), "<div class='header'></div>");
let htmldecoded: Vec = decodechars(&htmlencoded);
asserteq!(html, html_decoded.iter().collect::());
```
For more details, please see the document in Docs.rs
License
MIT License.