Added MultipartFile extractors.

Moved cfg macro to lib where possible.

Changed some features, and made some deps optional

src/serde/response.rs

@@ -1,15 +1,12 @@
-#[cfg(feature = "serde")]
 use serde::Serialize;
 
 #[derive(Serialize)]
-#[cfg(feature = "serde")]
 pub struct BaseResponse<T: Serialize> {
     pub version: String,
     #[serde(flatten)]
     pub body: T, // T must be a struct (or enum?)
 }
 
-#[cfg(feature = "serde")]
 impl<T: Serialize> BaseResponse<T> {
     pub fn new(version: impl Into<String>, body: T) -> Self {
         Self {
@@ -19,7 +16,7 @@ impl<T: Serialize> BaseResponse<T> {
     }
 }
 
-#[cfg(all(test, feature = "serde"))]
+#[cfg(test)]
 mod tests {
     use super::*;