Identifiers starting with a reserved keyword are treated as reserved keywords #29

First of all, thank you for this great library!

I noticed that dump() puts quotes around identifiers that only start with a reserved keyword. For example: internal_parameter would be dumped as "internal_parameter".

The issue seems to be in the regex that is created in lib._is_reserved_word(). Just appending $ to the whole pattern so that it reads _reserved_word_re = re.compile('|'.join(['break', ..., 'with']) + '$') fixes it.