Add int return values to MD5 function calls

The following function calls are being deprecated to introduce int
return values.
    * mbedtls_md5()
    * mbedtls_md5_starts()
    * mbedtls_md5_update()
    * mbedtls_md5_finish()
    * mbedtls_md5_process()
The return codes can be used to return error values. This is important
when using hardware accelerators.
diff --git a/include/mbedtls/md5.h b/include/mbedtls/md5.h
index 5a64061..7ecf49f 100644
--- a/include/mbedtls/md5.h
+++ b/include/mbedtls/md5.h
@@ -78,8 +78,10 @@
  * \brief          MD5 context setup
  *
  * \param ctx      context to be initialized
+ *
+ * \return         0 if successful
  */
-void mbedtls_md5_starts( mbedtls_md5_context *ctx );
+int mbedtls_md5_starts_ext( mbedtls_md5_context *ctx );
 
 /**
  * \brief          MD5 process buffer
@@ -87,19 +89,103 @@
  * \param ctx      MD5 context
  * \param input    buffer holding the  data
  * \param ilen     length of the input data
+ *
+ * \return         0 if successful
  */
-void mbedtls_md5_update( mbedtls_md5_context *ctx, const unsigned char *input, size_t ilen );
+int mbedtls_md5_update_ext( mbedtls_md5_context *ctx,
+                            const unsigned char *input,
+                            size_t ilen );
 
 /**
  * \brief          MD5 final digest
  *
  * \param ctx      MD5 context
  * \param output   MD5 checksum result
+ *
+ * \return         0 if successful
  */
-void mbedtls_md5_finish( mbedtls_md5_context *ctx, unsigned char output[16] );
+int mbedtls_md5_finish_ext( mbedtls_md5_context *ctx,
+                            unsigned char output[16] );
 
-/* Internal use */
-void mbedtls_md5_process( mbedtls_md5_context *ctx, const unsigned char data[64] );
+/**
+ * \brief          MD5 process data block (internal use only)
+ *
+ * \param ctx      MD5 context
+ * \param data     buffer holding one block of data
+ *
+ * \return         0 if successful
+ */
+int mbedtls_md5_process_ext( mbedtls_md5_context *ctx,
+                             const unsigned char data[64] );
+
+#if !defined(MBEDTLS_DEPRECATED_REMOVED)
+#if defined(MBEDTLS_DEPRECATED_WARNING)
+#define MBEDTLS_DEPRECATED      __attribute__((deprecated))
+#else
+#define MBEDTLS_DEPRECATED
+#endif
+/**
+ * \brief          MD5 context setup
+ *
+ * \deprecated     Superseded by mbedtls_md5_starts_ext() in 2.5.0
+ *
+ * \param ctx      context to be initialized
+ */
+MBEDTLS_DEPRECATED static inline void mbedtls_md5_starts(
+                                                    mbedtls_md5_context *ctx )
+{
+    mbedtls_md5_starts_ext( ctx );
+}
+
+/**
+ * \brief          MD5 process buffer
+ *
+ * \deprecated     Superseded by mbedtls_md5_update_ext() in 2.5.0
+ *
+ * \param ctx      MD5 context
+ * \param input    buffer holding the  data
+ * \param ilen     length of the input data
+ */
+MBEDTLS_DEPRECATED static inline void mbedtls_md5_update(
+                                                    mbedtls_md5_context *ctx,
+                                                    const unsigned char *input,
+                                                    size_t ilen )
+{
+    mbedtls_md5_update_ext( ctx, input, ilen );
+}
+
+/**
+ * \brief          MD5 final digest
+ *
+ * \deprecated     Superseded by mbedtls_md5_finish_ext() in 2.5.0
+ *
+ * \param ctx      MD5 context
+ * \param output   MD5 checksum result
+ */
+MBEDTLS_DEPRECATED static inline void mbedtls_md5_finish(
+                                                    mbedtls_md5_context *ctx,
+                                                    unsigned char output[16] )
+{
+    mbedtls_md5_finish_ext( ctx, output );
+}
+
+/**
+ * \brief          MD5 process data block (internal use only)
+ *
+ * \deprecated     Superseded by mbedtls_md5_process_ext() in 2.5.0
+ *
+ * \param ctx      MD5 context
+ * \param data     buffer holding one block of data
+ */
+MBEDTLS_DEPRECATED static inline void mbedtls_md5_process(
+                                                mbedtls_md5_context *ctx,
+                                                const unsigned char data[64] )
+{
+    mbedtls_md5_process_ext( ctx, data );
+}
+
+#undef MBEDTLS_DEPRECATED
+#endif /* !MBEDTLS_DEPRECATED_REMOVED */
 
 #ifdef __cplusplus
 }
@@ -119,8 +205,37 @@
  * \param input    buffer holding the  data
  * \param ilen     length of the input data
  * \param output   MD5 checksum result
+ *
+ * \return         0 if successful
  */
-void mbedtls_md5( const unsigned char *input, size_t ilen, unsigned char output[16] );
+int mbedtls_md5_ext( const unsigned char *input,
+                     size_t ilen,
+                     unsigned char output[16] );
+
+#if !defined(MBEDTLS_DEPRECATED_REMOVED)
+#if defined(MBEDTLS_DEPRECATED_WARNING)
+#define MBEDTLS_DEPRECATED      __attribute__((deprecated))
+#else
+#define MBEDTLS_DEPRECATED
+#endif
+/**
+ * \brief          Output = MD5( input buffer )
+ *
+ * \deprecated     Superseded by mbedtls_md5_ext() in 2.5.0
+ *
+ * \param input    buffer holding the  data
+ * \param ilen     length of the input data
+ * \param output   MD5 checksum result
+ */
+MBEDTLS_DEPRECATED static inline void mbedtls_md5( const unsigned char *input,
+                                                   size_t ilen,
+                                                   unsigned char output[16] )
+{
+    mbedtls_md5_ext( input, ilen, output );
+}
+
+#undef MBEDTLS_DEPRECATED
+#endif /* !MBEDTLS_DEPRECATED_REMOVED */
 
 /**
  * \brief          Checkup routine