Added an Error create.

src/morethantext/error.rs

@@ -0,0 +1,39 @@
+use std::{error::Error, fmt};
+
+#[derive(Debug)]
+pub struct MTTError {
+    detail: String,
+}
+
+impl MTTError {
+    fn new(detail: &str) -> Self {
+        Self {
+            detail: detail.to_string(),
+        }
+    }
+}
+
+impl fmt::Display for MTTError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}", self.detail)
+    }
+}
+
+impl Error for MTTError {}
+
+#[cfg(test)]
+mod errors {
+    use super::*;
+
+    #[test]
+    fn new_error() {
+        let detail = "new error";
+        let err = MTTError::new(detail);
+        assert!(
+            err.to_string() == detail,
+            "\n\nGot:  {}\nWant: {}\n\n",
+            err.to_string(),
+            detail
+        );
+    }
+}