py: Change uint to mp_uint_t in runtime.h, stackctrl.h, binary.h.

Part of code cleanup, working towards resolving issue #50.
diff --git a/py/builtinimport.c b/py/builtinimport.c
index fa3bcde..ec29f52 100644
--- a/py/builtinimport.c
+++ b/py/builtinimport.c
@@ -165,7 +165,7 @@
     mp_globals_set(old_globals);
 }
 
-mp_obj_t mp_builtin___import__(uint n_args, mp_obj_t *args) {
+mp_obj_t mp_builtin___import__(mp_uint_t n_args, mp_obj_t *args) {
 #if DEBUG_PRINT
     printf("__import__:\n");
     for (int i = 0; i < n_args; i++) {