Expose limiting for * and + in Xeger.xeger()

[crackhead-koala]

Hello!

Thank you for this library, it has been very helpful for me in my project. However, I found that the Xeger.xeger() method lacks control over how many characters are generated from a regexp by * and + metacharacters.

This pull request adds the second argument star_plus_limit to this method with the default value of 100. It also removes the constant STAR_PLUS_LIMIT as it is no longer needed.

[bjmc]

Thanks for this pull request! Can you explain a little bit more about your use case? Rather than adding another parameter to the xeger() method, why not specify the number of repeats you want in the regular expression?

For example if you wanted to generate up to 500 repetitions of a you could use a{1,500}. Would that work for your situation?

[crackhead-koala]

I mostly need comparatively shorts strings from regular expressions, at most 10 characters, so setting this limit in every regex is a bit cumbersome.