[Suggestion] Use "REQUEST_PATH" Instead of "SCRIPT_NAME" to Get Requested URI

[loloicci]

I suggest using REQUEST_PATH instead of SCRIPT_NAME to get requested URI in parse_request.

https://github.com/rory/rust-cgi/blob/269b6680b84bc2645e89ec144f31bbc8b7a4bb2a/src/lib.rs#L235-L240

When the server uses mod_rewrite and rewrite requested URI:

• If we use SCRIPT_NAME to get URI, the requested URI before rewriting is lost.
• If we use REQUEST_PATH to get URI, gotten URI is the same one before rewriting.