feature/esp_http_client:Changes to make esp_http_client compatible with ESP8266.

Changes:
Added rom/md5_hash.h.
Example code & sdkconfig.defaults changed for compatibility.
Changed component.mk to enable compilation only for mbedtls.

components/esp8266/include/rom/md5_hash.h

@@ -0,0 +1,38 @@
+/*
+ * MD5 internal definitions
+ * Copyright (c) 2003-2005, Jouni Malinen <j@w1.fi>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * Alternatively, this software may be distributed under the terms of BSD
+ * license.
+ *
+ * See README and COPYING for more details.
+ */
+
+#ifndef _ROM_MD5_HASH_H_
+#define _ROM_MD5_HASH_H_
+
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+struct MD5Context {
+	uint32_t buf[4];
+	uint32_t bits[2];
+	uint8_t in[64];
+};
+
+void MD5Init(struct MD5Context *context);
+void MD5Update(struct MD5Context *context, unsigned char const *buf, unsigned len);
+void MD5Final(unsigned char digest[16], struct MD5Context *context);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* _ROM_MD5_HASH_H_ */