Add ability to get all common sequences

src/utils.rs

@@ -0,0 +1,12 @@
+pub fn slice_str(string: &str, start: usize, end: usize) -> Option<&str>
+{
+	if start >= end{
+	    return None
+    }
+    if start > string.len() || end > string.len(){
+    	return None
+    }
+    unsafe{
+    	Some(string.slice_unchecked(start, end))
+    }
+}