feat(str): Add some string manipulation utilities

src/str.rs

+const SEPARATORS: &[char] = &[' ', '_', '-'];
+
+pub fn to_train_case<S: AsRef<str>>(input: S) -> String {
+    let items: Vec<String> = String::from(input.as_ref())
+        .split(SEPARATORS)
+        .map(ToString::to_string)
+        .collect();
+
+    items.join("_").to_uppercase()
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_to_train_case() -> () {
+        assert_eq!(to_train_case("omg-OMG_omg123 omg"), "OMG_OMG_OMG123_OMG")
+    }
+}