Refactor users management (#7)

* Improve general settings management by admin

src/utils/err.rs

@@ -1,2 +1,34 @@
 use std::error::Error;
+use std::fmt;
+use std::fmt::{Display, Formatter};
+
 pub type Res<A = ()> = Result<A, Box<dyn Error>>;
+
+#[derive(Debug, Clone)]
+pub struct ExecError(pub String);
+
+impl ExecError {
+    pub fn new(msg: &str) -> ExecError {
+        ExecError(msg.to_string())
+    }
+
+    pub fn boxed_new<D: Display>(msg: D) -> Box<ExecError> {
+        Box::new(ExecError(msg.to_string()))
+    }
+
+    pub fn boxed_string(msg: String) -> Box<ExecError> {
+        Box::new(ExecError(msg))
+    }
+}
+
+impl Display for ExecError {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        write!(f, "Encountered error: {}", self.0)
+    }
+}
+
+impl Error for ExecError {}
+
+pub fn new_error<D: Display>(msg: D) -> Res {
+    Err(ExecError::boxed_new(msg))
+}