Replace methods with more flexible endpoints

tests/ui/from_body/enum.rs

@@ -0,0 +1,10 @@
+#[macro_use]
+extern crate gotham_restful;
+
+#[derive(FromBody)]
+enum FromBodyEnum {
+	SomeVariant(Vec<u8>),
+	OtherVariant(String)
+}
+
+fn main() {}

tests/ui/from_body/enum.stderr

@@ -0,0 +1,5 @@
+error: #[derive(FromBody)] only works for structs
+ --> $DIR/enum.rs:5:1
+  |
+5 | enum FromBodyEnum {
+  | ^^^^