extrakeys: Init empty experimental module

This is to prepare for xonly_pubkeys and keypairs.

src/modules/extrakeys/Makefile.am.include

@@ -0,0 +1,3 @@
+include_HEADERS += include/secp256k1_extrakeys.h
+noinst_HEADERS += src/modules/extrakeys/tests_impl.h
+noinst_HEADERS += src/modules/extrakeys/main_impl.h

src/modules/extrakeys/main_impl.h

@@ -0,0 +1,13 @@
+/**********************************************************************
+ * Copyright (c) 2020 Jonas Nick                                      *
+ * Distributed under the MIT software license, see the accompanying   *
+ * file COPYING or http://www.opensource.org/licenses/mit-license.php.*
+ **********************************************************************/
+
+#ifndef _SECP256K1_MODULE_EXTRAKEYS_MAIN_
+#define _SECP256K1_MODULE_EXTRAKEYS_MAIN_
+
+#include "include/secp256k1.h"
+#include "include/secp256k1_extrakeys.h"
+
+#endif

src/modules/extrakeys/tests_impl.h

@@ -0,0 +1,16 @@
+/**********************************************************************
+ * Copyright (c) 2020 Jonas Nick                                      *
+ * Distributed under the MIT software license, see the accompanying   *
+ * file COPYING or http://www.opensource.org/licenses/mit-license.php.*
+ **********************************************************************/
+
+#ifndef _SECP256K1_MODULE_EXTRAKEYS_TESTS_
+#define _SECP256K1_MODULE_EXTRAKEYS_TESTS_
+
+#include "secp256k1_extrakeys.h"
+
+void run_extrakeys_tests(void) {
+    /* TODO */
+}
+
+#endif

src/secp256k1.c

@@ -742,3 +742,7 @@ int secp256k1_ec_pubkey_combine(const secp256k1_context* ctx, secp256k1_pubkey *
 #ifdef ENABLE_MODULE_RECOVERY
 # include "modules/recovery/main_impl.h"
 #endif
+
+#ifdef ENABLE_MODULE_EXTRAKEYS
+# include "modules/extrakeys/main_impl.h"
+#endif

src/tests.c

@@ -5306,6 +5306,10 @@ void run_ecdsa_openssl(void) {
 # include "modules/recovery/tests_impl.h"
 #endif
 
+#ifdef ENABLE_MODULE_EXTRAKEYS
+# include "modules/extrakeys/tests_impl.h"
+#endif
+
 void run_memczero_test(void) {
     unsigned char buf1[6] = {1, 2, 3, 4, 5, 6};
     unsigned char buf2[sizeof(buf1)];
@@ -5612,6 +5616,10 @@ int main(int argc, char **argv) {
     run_recovery_tests();
 #endif
 
+#ifdef ENABLE_MODULE_EXTRAKEYS
+    run_extrakeys_tests();
+#endif
+
     /* util tests */
     run_memczero_test();