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/parse.h

@@ -63,5 +63,11 @@ typedef enum {
     MP_PARSE_EVAL_INPUT,
 } mp_parse_input_kind_t;
 
-// returns MP_PARSE_NODE_NULL on error, and then exc_id_out and exc_msg_out are valid
-mp_parse_node_t mp_parse(struct _mp_lexer_t *lex, mp_parse_input_kind_t input_kind, qstr *exc_id_out, const char **exc_msg_out);
+typedef enum {
+    MP_PARSE_ERROR_UNEXPECTED_INDENT,
+    MP_PARSE_ERROR_UNMATCHED_UNINDENT,
+    MP_PARSE_ERROR_INVALID_SYNTAX,
+} mp_parse_error_kind_t;
+
+// returns MP_PARSE_NODE_NULL on error, and then parse_error_kind_out is valid
+mp_parse_node_t mp_parse(struct _mp_lexer_t *lex, mp_parse_input_kind_t input_kind, mp_parse_error_kind_t *parse_error_kind_out);