Unhelpful error message 'msg' when `_expect` fails

[ulope]

When _Source._expect() fails it raises a TomlError with the unhelpful error message msg:

pytoml/pytoml/parser.py

Line 164 in cb92445

raise TomlError('msg', self._pos[0], self._pos[1], self._filename)

Example to provoke this error:

[a]b

[MarSoft]

Same problem.