add support for casbin@0.3.0

[GopherJ]

Currently diesel-adapter doesn't support casbin@0.3.0 because of breaking changes on Adapter trait.

Now it has tow more functions:

1. remove_policies
2. add_policies

#[async_trait]
pub trait Adapter: Send + Sync {
    async fn load_policy(&self, m: &mut dyn Model) -> Result<()>;
    async fn save_policy(&mut self, m: &mut dyn Model) -> Result<()>;
    async fn add_policy(&mut self, sec: &str, ptype: &str, rule: Vec<&str>) -> Result<bool>;
    async fn add_policies(&mut self, sec: &str, ptype: &str, rules: Vec<Vec<&str>>)
        -> Result<bool>;
    async fn remove_policy(&mut self, sec: &str, ptype: &str, rule: Vec<&str>) -> Result<bool>;
    async fn remove_policies(
        &mut self,
        sec: &str,
        ptype: &str,
        rules: Vec<Vec<&str>>,
    ) -> Result<bool>;
    async fn remove_filtered_policy(
        &mut self,
        sec: &str,
        ptype: &str,
        field_index: usize,
        field_values: Vec<&str>,
    ) -> Result<bool>;
}

see also: casbin/casbin-rs#55