fix(errors): Report errors on unknown #[serde(...)] attributes

Closes #51, #175, and #187

serde_macros/tests/compile-fail/reject-unknown-attributes.rs

@@ -0,0 +1,30 @@
+#![feature(custom_attribute, custom_derive, plugin)]
+#![plugin(serde_macros)]
+
+extern crate serde;
+
+#[derive(Serialize)]
+#[serde(abc="xyz")] //~ unknown serde container attribute `abc = "xyz"`
+struct Foo {
+    x: u32,
+}
+
+#[derive(Deserialize)]
+#[serde(abc="xyz")] //~ unknown serde container attribute `abc = "xyz"`
+struct Foo {
+    x: u32,
+}
+
+#[derive(Serialize)]
+struct Foo {
+    #[serde(abc="xyz")] //~ unknown serde field attribute `abc = "xyz"`
+    x: u32,
+}
+
+#[derive(Deserialize)]
+struct Foo {
+    #[serde(abc="xyz")] //~ unknown serde field attribute `abc = "xyz"`
+    x: u32,
+}
+
+fn main() { }