Update demos

To build demos, run
`cmake .. -DENABLE_DEMOS=ON`

demos/src/x509_crl_find_revoked_cert_demo.c

@@ -0,0 +1,68 @@
+/*
+ *  Copyright 2014-2023 The GmSSL Project. All Rights Reserved.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the License); you may
+ *  not use this file except in compliance with the License.
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <gmssl/file.h>
+#include <gmssl/x509_crl.h>
+
+// 为了这些demo，应该准备好测试的文件，而不是把文件都放在源代码里面
+// 这样会更灵活一些
+
+int main(int argc, char **argv)
+{
+	int ret = -1;
+
+	uint8_t *crl;
+	size_t crllen;
+
+	char *cert;
+	size_t certlen;
+
+	const uint8_t *cert_serial;
+	size_t cert_serial_len;
+	time_t cert_revoke_date;
+	const uint8_t *crl_entry_exts;
+	size_t crl_entry_exts_len;
+
+	int revoked;
+
+	printf("Demo - Check if a Certificate has been revoked in a CRL\n");
+
+
+	if (x509_cert_get_issuer_and_serial_number(cert, certlen,
+		NULL, NULL, &cert_serial, &cert_serial_len) != 1) {
+		fprintf(stderr, "x509_cert_get_issuer_and_serial_number() error\n");
+		goto err;
+	}
+
+	if ((revoked = x509_crl_find_revoked_cert_by_serial_number(
+		crl, crllen,
+		cert_serial, cert_serial_len,
+		&cert_revoked_date,
+		&crl_entry_exts, &crl_entry_exts_len)) == -1) {
+
+		fprintf(stderr, "x509_crl_find_revoked_cert_by_serial_number() error\n");
+		goto err;
+	}
+
+	if (revoked) {
+		printf("    The certificate has been revoked\n");
+		format_bytes(stderr, 0, 4, "SerialNumber", cert_serial, cert_serial_len);
+		x509_crl_entry_exts_print(stderr, 0, 4, "CRLEntryExts", crl_entry_exts, crl_entry_exts_len);
+	} else {
+		printf("    The certificate not in the given CRL\n");
+	}
+
+	ret = 0;
+err:
+	if (der) free(der);
+	return ret;
+}