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.
diff --git a/py/builtinevex.c b/py/builtinevex.c
index 3e3c9a6..6e920e8 100644
--- a/py/builtinevex.c
+++ b/py/builtinevex.c
@@ -13,6 +13,7 @@
 #include "lexerunix.h"
 #include "parse.h"
 #include "obj.h"
+#include "parsehelper.h"
 #include "compile.h"
 #include "runtime0.h"
 #include "runtime.h"
@@ -28,14 +29,13 @@
     qstr source_name = mp_lexer_source_name(lex);
 
     // parse the string
-    qstr parse_exc_id;
-    const char *parse_exc_msg;
-    mp_parse_node_t pn = mp_parse(lex, parse_input_kind, &parse_exc_id, &parse_exc_msg);
+    mp_parse_error_kind_t parse_error_kind;
+    mp_parse_node_t pn = mp_parse(lex, parse_input_kind, &parse_error_kind);
     mp_lexer_free(lex);
 
     if (pn == MP_PARSE_NODE_NULL) {
         // parse error; raise exception
-        nlr_jump(mp_obj_new_exception_msg(parse_exc_id, parse_exc_msg));
+        nlr_jump(mp_parse_make_exception(parse_error_kind));
     }
 
     // compile the string
@@ -74,6 +74,7 @@
         rt_locals_set(mp_obj_dict_get_map(locals));
     }
     mp_obj_t res = parse_compile_execute(args[0], MP_PARSE_FILE_INPUT);
+    // TODO if the above call throws an exception, then we never get to reset the globals/locals
     rt_globals_set(old_globals);
     rt_locals_set(old_locals);
     return res;