Rename time and index parameter to avoid name conflict.

As noted in #557, several functions use 'index' resp. 'time'
as parameter names in their declaration and/or definition, causing name
conflicts with the functions in the C standard library of the same
name some compilers warn about.

This commit renames the arguments accordingly.
diff --git a/include/mbedtls/ecp.h b/include/mbedtls/ecp.h
index 723e46c..ef65326 100644
--- a/include/mbedtls/ecp.h
+++ b/include/mbedtls/ecp.h
@@ -437,7 +437,7 @@
  * \brief           Set a group using well-known domain parameters
  *
  * \param grp       Destination group
- * \param index     Index in the list of well-known domain parameters
+ * \param id        Index in the list of well-known domain parameters
  *
  * \return          0 if successful,
  *                  MBEDTLS_ERR_MPI_XXX if initialization failed
@@ -446,7 +446,7 @@
  * \note            Index should be a value of RFC 4492's enum NamedCurve,
  *                  usually in the form of a MBEDTLS_ECP_DP_XXX macro.
  */
-int mbedtls_ecp_group_load( mbedtls_ecp_group *grp, mbedtls_ecp_group_id index );
+int mbedtls_ecp_group_load( mbedtls_ecp_group *grp, mbedtls_ecp_group_id id );
 
 /**
  * \brief           Set a group from a TLS ECParameters record