Add new test file with icode. Add test to parse it

tests/test.rs

@@ -49,6 +49,14 @@ mod test_f2 {
     }
 }
 
+#[test]
+fn parse_f2_icode() {
+    let my_struct = parser::read_pdb("tests/tests_file/f2_icode.pdb", "f2");
+    assert_eq!(1, my_struct.get_chain_number());
+    assert_eq!(67, my_struct.get_residue_number());
+    assert_eq!(1096, my_struct.get_atom_number());
+}
+
 #[test]
 fn parse_f2_adn() {
     let my_struct = parser::read_pdb("tests/tests_file/f2_adn.pdb", "f2");