Implement ROMable modules. Add math module.
mp_module_obj_t can now be put in ROM.
Configuration of float type is now similar to longint: can now choose
none, float or double as the implementation.
math module has basic math functions. For STM port, these are not yet
implemented (they are just stub functions).
diff --git a/py/builtin.h b/py/builtin.h
index 85ceeaf..d941404 100644
--- a/py/builtin.h
+++ b/py/builtin.h
@@ -34,4 +34,5 @@
MP_DECLARE_CONST_FUN_OBJ(mp_namedtuple_obj);
-void mp_module_micropython_init(void);
+extern const mp_obj_module_t mp_module_math;
+extern const mp_obj_module_t mp_module_micropython;