Add new option: x264-crf ( #330

Fix typo in x264-profile option handle

src/opt/crf.rs

@@ -0,0 +1,8 @@
+use json::JsonValue;
+
+pub fn check_crf(obj: &JsonValue) -> bool {
+    match obj.as_f32() {
+        Some(crf) => crf >= -1f32,
+        None => false,
+    }
+}