Add parse_instruction()

Same as the parse_orientation() function but for the instruction model

src/main.rs

@@ -21,6 +21,15 @@ fn parse_orientation(c: char) -> Option<Orientation> {
     }
 }
 
+fn parse_instruction(c: char) -> Option<Instruction> {
+    match c {
+        'L' => Some(Instruction::L),
+        'R' => Some(Instruction::R),
+        'F' => Some(Instruction::F),
+        _ => None,
+    }
+}
+
 fn main() {
     let file_data = include_str!("../two_robots.txt");
 }