Add clippy (#191)

* Organize imports

Use rustfmt to organize imports.  Resolve #162

* remove unused imports

* Fix clippy complaints

* add clippy github action

* remove comment for @arnaucube

src/middleware/custom.rs

@@ -201,10 +201,9 @@ impl ToFields for StatementTmpl {
 }
 
 #[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize, JsonSchema)]
+/// NOTE: fields are not public (outside of crate) to enforce the struct instantiation through
+/// the `::and/or` methods, which performs checks on the values.
 pub struct CustomPredicate {
-    /// NOTE: fields are not public (outside of crate) to enforce the struct instantiation through
-    /// the `::and/or` methods, which performs checks on the values.
-
     /// true for "and", false for "or"
     pub(crate) conjunction: bool,
     pub(crate) statements: Vec<StatementTmpl>,