Change object representation from 1 big union to individual structs.

A big change.  Micro Python objects are allocated as individual structs
with the first element being a pointer to the type information (which
is itself an object).  This scheme follows CPython.  Much more flexible,
not necessarily slower, uses same heap memory, and can allocate objects
statically.

Also change name prefix, from py_ to mp_ (mp for Micro Python).

py/objbool.c

@@ -0,0 +1,39 @@
+#include <stdlib.h>
+#include <stdint.h>
+
+#include "nlr.h"
+#include "misc.h"
+#include "mpconfig.h"
+#include "obj.h"
+
+typedef struct _mp_obj_bool_t {
+    mp_obj_base_t base;
+    bool value;
+} mp_obj_bool_t;
+
+void bool_print(void (*print)(void *env, const char *fmt, ...), void *env, mp_obj_t self_in) {
+    mp_obj_bool_t *self = self_in;
+    if (self->value) {
+        print(env, "True");
+    } else {
+        print(env, "False");
+    }
+}
+
+const mp_obj_type_t bool_type = {
+    { &mp_const_type },
+    "bool",
+    bool_print, // print
+    NULL, // call_n
+    NULL, // unary_op
+    NULL, // binary_op
+    NULL, // getiter
+    NULL, // iternext
+    {{NULL, NULL},}, // method list
+};
+
+static const mp_obj_bool_t false_obj = {{&bool_type}, false};
+static const mp_obj_bool_t true_obj = {{&bool_type}, true};
+
+const mp_obj_t mp_const_false = (mp_obj_t)&false_obj;
+const mp_obj_t mp_const_true = (mp_obj_t)&true_obj;