Generate htpasswd files with bcrypt passwords.

Example

```rust use std::error::Error; use passivizedhtpasswd::errors::HtpasswdError; use passivizedhtpasswd::Htpasswd;

fn setup_credentials() -> Result<(), Box> { let mut credentials = Htpasswd::new();

credentials.set("John Doe", "Don't hardcode")?;
credentials.write_to_path("www/.htpasswd")?;

Ok(())

} ```