Implement proper exception type hierarchy.

Each built-in exception is now a type, with base type BaseException.
C exceptions are created by passing a pointer to the exception type to
make an instance of.  When raising an exception from the VM, an
instance is created automatically if an exception type is raised (as
opposed to an exception instance).

Exception matching (RT_BINARY_OP_EXCEPTION_MATCH) is now proper.

Handling of parse error changed to match new exceptions.

mp_const_type renamed to mp_type_type for consistency.

py/objint.c

@@ -39,7 +39,7 @@ STATIC mp_obj_t int_make_new(mp_obj_t type_in, uint n_args, uint n_kw, const mp_
         }
 
         default:
-            nlr_jump(mp_obj_new_exception_msg_varg(MP_QSTR_TypeError, "int takes at most 2 arguments, %d given", n_args));
+            nlr_jump(mp_obj_new_exception_msg_varg(&mp_type_TypeError, "int takes at most 2 arguments, %d given", n_args));
     }
 }
 
@@ -65,7 +65,7 @@ mp_obj_t int_binary_op(int op, mp_obj_t lhs_in, mp_obj_t rhs_in) {
 
 // This is called only with strings whose value doesn't fit in SMALL_INT
 mp_obj_t mp_obj_new_int_from_long_str(const char *s) {
-    nlr_jump(mp_obj_new_exception_msg(MP_QSTR_OverflowError, "long int not supported in this build"));
+    nlr_jump(mp_obj_new_exception_msg(&mp_type_OverflowError, "long int not supported in this build"));
     return mp_const_none;
 }
 
@@ -75,7 +75,7 @@ mp_obj_t mp_obj_new_int_from_uint(machine_uint_t value) {
     if ((value & (WORD_MSBIT_HIGH | (WORD_MSBIT_HIGH >> 1))) == 0) {
         return MP_OBJ_NEW_SMALL_INT(value);
     }
-    nlr_jump(mp_obj_new_exception_msg(MP_QSTR_OverflowError, "small int overflow"));
+    nlr_jump(mp_obj_new_exception_msg(&mp_type_OverflowError, "small int overflow"));
     return mp_const_none;
 }
 
@@ -83,7 +83,7 @@ mp_obj_t mp_obj_new_int(machine_int_t value) {
     if (MP_OBJ_FITS_SMALL_INT(value)) {
         return MP_OBJ_NEW_SMALL_INT(value);
     }
-    nlr_jump(mp_obj_new_exception_msg(MP_QSTR_OverflowError, "small int overflow"));
+    nlr_jump(mp_obj_new_exception_msg(&mp_type_OverflowError, "small int overflow"));
     return mp_const_none;
 }
 
@@ -98,7 +98,7 @@ machine_int_t mp_obj_int_get_checked(mp_obj_t self_in) {
 #endif // MICROPY_LONGINT_IMPL == MICROPY_LONGINT_IMPL_NONE
 
 const mp_obj_type_t int_type = {
-    { &mp_const_type },
+    { &mp_type_type },
     .name = MP_QSTR_int,
     .print = int_print,
     .make_new = int_make_new,