move prehashed enum to common; downside is that including one eddsa.hxx now pulls in all of them

src/per_curve/eddsa.tmpl.hxx

@@ -7,6 +7,7 @@
  * @warning Experimental!  The names, parameter orders etc are likely to change.
  */
 
+#include <decaf/eddsa.hxx>
 #include <decaf/decaf_$(gf_bits).hxx>
 #include <decaf/eddsa_$(gf_bits).h>
 
@@ -28,8 +29,6 @@ template <typename Group> struct EdDSA;
 
 /** A public key for crypto over $(name) */
 template<> struct EdDSA<$(cxx_ns)> {
-    
-enum Prehashed { PURE, PREHASHED };
 
 /** @cond internal */
 template<class CRTP, Prehashed> class Signing;

src/public_include/decaf/eddsa.tmpl.hxx

@@ -2,6 +2,7 @@
  * EdDSA crypto routines, metaheader.
  */
 
+namespace decaf { enum Prehashed { PURE, PREHASHED }; }
 $("\n".join([
     "#include <decaf/eddsa_%s.hxx>" % g for g in sorted([c["bits"] for _,c in curve.iteritems()])
 ]))