crate-only several BOLT12 methods that require unbounded generics

These are not expressible in C/most languages, and thus must be
hidden.

lightning/src/offers/invoice.rs

@@ -424,7 +424,7 @@ impl UnsignedBolt12Invoice {
 	/// Note: The hash computation may have included unknown, odd TLV records.
 	///
 	/// This is not exported to bindings users as functions aren't currently mapped.
-	pub fn sign<F, E>(mut self, sign: F) -> Result<Bolt12Invoice, SignError<E>>
+	pub(crate) fn sign<F, E>(mut self, sign: F) -> Result<Bolt12Invoice, SignError<E>>
 	where
 		F: FnOnce(&Self) -> Result<Signature, E>
 	{

lightning/src/offers/invoice_request.rs

@@ -395,7 +395,7 @@ impl UnsignedInvoiceRequest {
 	/// Note: The hash computation may have included unknown, odd TLV records.
 	///
 	/// This is not exported to bindings users as functions are not yet mapped.
-	pub fn sign<F, E>(mut self, sign: F) -> Result<InvoiceRequest, SignError<E>>
+	pub(crate) fn sign<F, E>(mut self, sign: F) -> Result<InvoiceRequest, SignError<E>>
 	where
 		F: FnOnce(&Self) -> Result<Signature, E>
 	{

lightning/src/offers/merkle.rs

@@ -76,7 +76,7 @@ impl AsRef<TaggedHash> for TaggedHash {
 
 /// Error when signing messages.
 #[derive(Debug, PartialEq)]
-pub enum SignError<E> {
+pub(crate) enum SignError<E> {
 	/// User-defined error when signing the message.
 	Signing(E),
 	/// Error when verifying the produced signature using the given pubkey.