py: Add math.e constant.
diff --git a/py/builtinmath.c b/py/builtinmath.c
index eeb7150..661638b 100644
--- a/py/builtinmath.c
+++ b/py/builtinmath.c
@@ -17,6 +17,7 @@
     mp_obj_t mp_math_ ## py_name(mp_obj_t x_obj, mp_obj_t y_obj) { return mp_obj_new_float(MICROPY_FLOAT_C_FUN(c_name)(mp_obj_get_float(x_obj), mp_obj_get_float(y_obj))); } \
     STATIC MP_DEFINE_CONST_FUN_OBJ_2(mp_math_## py_name ## _obj, mp_math_ ## py_name);
 
+STATIC const mp_obj_float_t mp_math_e_obj = {{&mp_type_float}, M_E};
 STATIC const mp_obj_float_t mp_math_pi_obj = {{&mp_type_float}, M_PI};
 
 MATH_FUN_1(sqrt, sqrt)
@@ -42,6 +43,7 @@
 
 STATIC const mp_map_elem_t mp_module_math_globals_table[] = {
     { MP_OBJ_NEW_QSTR(MP_QSTR___name__), MP_OBJ_NEW_QSTR(MP_QSTR_math) },
+    { MP_OBJ_NEW_QSTR(MP_QSTR_e), (mp_obj_t)&mp_math_e_obj },
     { MP_OBJ_NEW_QSTR(MP_QSTR_pi), (mp_obj_t)&mp_math_pi_obj },
     { MP_OBJ_NEW_QSTR(MP_QSTR_sqrt), (mp_obj_t)&mp_math_sqrt_obj },
     { MP_OBJ_NEW_QSTR(MP_QSTR_pow), (mp_obj_t)&mp_math_pow_obj },