Rename _wrap headers to _internal

Makes it clearer that the user is not supposed to include them
diff --git a/include/mbedtls/md_internal.h b/include/mbedtls/md_internal.h
new file mode 100644
index 0000000..d42dc5c
--- /dev/null
+++ b/include/mbedtls/md_internal.h
@@ -0,0 +1,115 @@
+/**
+ * \file md_internal.h
+ *
+ * \brief Message digest wrappers.
+ *
+ * \warning This in an internal header. Do not include directly.
+ *
+ * \author Adriaan de Jong <dejong@fox-it.com>
+ *
+ *  Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
+ *
+ *  This file is part of mbed TLS (https://tls.mbed.org)
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License along
+ *  with this program; if not, write to the Free Software Foundation, Inc.,
+ *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+#ifndef MBEDTLS_MD_WRAP_H
+#define MBEDTLS_MD_WRAP_H
+
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
+#include "md.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * Message digest information.
+ * Allows message digest functions to be called in a generic way.
+ */
+struct mbedtls_md_info_t
+{
+    /** Digest identifier */
+    mbedtls_md_type_t type;
+
+    /** Name of the message digest */
+    const char * name;
+
+    /** Output length of the digest function */
+    int size;
+
+    /** Block length of the digest function */
+    int block_size;
+
+    /** Digest initialisation function */
+    void (*starts_func)( void *ctx );
+
+    /** Digest update function */
+    void (*update_func)( void *ctx, const unsigned char *input, size_t ilen );
+
+    /** Digest finalisation function */
+    void (*finish_func)( void *ctx, unsigned char *output );
+
+    /** Generic digest function */
+    void (*digest_func)( const unsigned char *input, size_t ilen,
+                         unsigned char *output );
+
+    /** Generic file digest function */
+    int (*file_func)( const char *path, unsigned char *output );
+
+    /** Allocate a new context */
+    void * (*ctx_alloc_func)( void );
+
+    /** Free the given context */
+    void (*ctx_free_func)( void *ctx );
+
+    /** Internal use only */
+    void (*process_func)( void *ctx, const unsigned char *input );
+};
+
+#if defined(MBEDTLS_MD2_C)
+extern const mbedtls_md_info_t mbedtls_md2_info;
+#endif
+#if defined(MBEDTLS_MD4_C)
+extern const mbedtls_md_info_t mbedtls_md4_info;
+#endif
+#if defined(MBEDTLS_MD5_C)
+extern const mbedtls_md_info_t mbedtls_md5_info;
+#endif
+#if defined(MBEDTLS_RIPEMD160_C)
+extern const mbedtls_md_info_t mbedtls_ripemd160_info;
+#endif
+#if defined(MBEDTLS_SHA1_C)
+extern const mbedtls_md_info_t mbedtls_sha1_info;
+#endif
+#if defined(MBEDTLS_SHA256_C)
+extern const mbedtls_md_info_t mbedtls_sha224_info;
+extern const mbedtls_md_info_t mbedtls_sha256_info;
+#endif
+#if defined(MBEDTLS_SHA512_C)
+extern const mbedtls_md_info_t mbedtls_sha384_info;
+extern const mbedtls_md_info_t mbedtls_sha512_info;
+#endif
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* MBEDTLS_MD_WRAP_H */