all: Raise exceptions via mp_raise_XXX

- Changed: ValueError, TypeError, NotImplementedError
  - OSError invocations unchanged, because the corresponding utility
    function takes ints, not strings like the long form invocation.
  - OverflowError, IndexError and RuntimeError etc. not changed for now
    until we decide whether to add new utility functions.

py/lexer.c

@@ -341,7 +341,7 @@ STATIC void parse_string_literal(mp_lexer_t *lex, bool is_raw) {
                             // 3MB of text; even gzip-compressed and with minimal structure, it'll take
                             // roughly half a meg of storage. This form of Unicode escape may be added
                             // later on, but it's definitely not a priority right now. -- CJA 20140607
-                            mp_not_implemented("unicode name escapes");
+                            mp_raise_NotImplementedError("unicode name escapes");
                             break;
                         default:
                             if (c >= '0' && c <= '7') {