change local lib headers to be relative for those pointing at "include/" dir

added relative paths to header files imported from src directory

added include guards for contrib/ files when referring to secp256k1.h

src/modules/recovery/main_impl.h

@@ -7,7 +7,7 @@
 #ifndef SECP256K1_MODULE_RECOVERY_MAIN_H
 #define SECP256K1_MODULE_RECOVERY_MAIN_H
 
-#include "include/secp256k1_recovery.h"
+#include "../../../include/secp256k1_recovery.h"
 
 static void secp256k1_ecdsa_recoverable_signature_load(const secp256k1_context* ctx, secp256k1_scalar* r, secp256k1_scalar* s, int* recid, const secp256k1_ecdsa_recoverable_signature* sig) {
     (void)ctx;

src/modules/recovery/tests_exhaustive_impl.h

@@ -8,7 +8,7 @@
 #define SECP256K1_MODULE_RECOVERY_EXHAUSTIVE_TESTS_H
 
 #include "src/modules/recovery/main_impl.h"
-#include "include/secp256k1_recovery.h"
+#include "../../../include/secp256k1_recovery.h"
 
 void test_exhaustive_recovery_sign(const secp256k1_context *ctx, const secp256k1_ge *group) {
     int i, j, k;