Parse unsafety on function signatures
diff --git a/syntax/mod.rs b/syntax/mod.rs
index 03422d1..f52a582 100644
--- a/syntax/mod.rs
+++ b/syntax/mod.rs
@@ -87,6 +87,7 @@
 }
 
 pub struct Signature {
+    pub unsafety: Option<Token![unsafe]>,
     pub fn_token: Token![fn],
     pub receiver: Option<Receiver>,
     pub args: Punctuated<Var, Token![,]>,