rangeproof: several API changes

* add summing function for blinded generators
* drop `excess` and `gen` from `verify_tally`
* add extra_commit to rangeproof sign and verify

src/modules/generator/main_impl.h

@@ -12,6 +12,7 @@
 #include "field.h"
 #include "group.h"
 #include "hash.h"
+#include "scalar.h"
 
 static void secp256k1_generator_load(secp256k1_ge* ge, const secp256k1_generator* gen) {
     secp256k1_fe fe;