Change the hashcounts in raw Lit variants from usize to u16.

This reduces the size of `Token` from 32 bytes to 24 bytes on 64-bit
platforms.

src/libsyntax/ast.rs

@@ -1260,8 +1260,8 @@ pub enum StrStyle {
     Cooked,
     /// A raw string, like `r##"foo"##`
     ///
-    /// The uint is the number of `#` symbols used
-    Raw(usize)
+    /// The value is the number of `#` symbols used.
+    Raw(u16)
 }
 
 /// A literal