Replace methods with more flexible endpoints

tests/ui/endpoint/self.stderr

@@ -0,0 +1,19 @@
+error: Didn't expect self parameter
+ --> $DIR/self.rs:9:13
+  |
+9 | fn read_all(self) {}
+  |             ^^^^
+
+error: `self` parameter is only allowed in associated functions
+ --> $DIR/self.rs:9:13
+  |
+9 | fn read_all(self) {}
+  |             ^^^^ not semantically valid as function parameter
+  |
+  = note: associated functions are those in `impl` or `trait` definitions
+
+error[E0412]: cannot find type `read_all___gotham_restful_endpoint` in this scope
+ --> $DIR/self.rs:5:12
+  |
+5 | #[resource(read_all)]
+  |            ^^^^^^^^ not found in this scope