Allow to forward declare of public structs #1215

Thanks to forward declare we can declare `struct` in our header file instead making #include
diff --git a/include/mbedtls/camellia.h b/include/mbedtls/camellia.h
index 7e4721a..fa1e05e 100644
--- a/include/mbedtls/camellia.h
+++ b/include/mbedtls/camellia.h
@@ -51,7 +51,7 @@
 /**
  * \brief          CAMELLIA context structure
  */
-typedef struct
+typedef struct mbedtls_camellia_context
 {
     int nr;                     /*!<  number of rounds  */
     uint32_t rk[68];            /*!<  CAMELLIA round keys    */