no while checks if scanning a capture

[msftrncs]

This is a possible solution to #87. This prevents _tokenizeString from performing a while rule check if the starting line position is not 0 upon entry to the function.

Maybe it would be better if _tokenizeString was not responsible for performing the while rules check, and it was instead performed by _tokenize, since _tokenize is always starting a fresh line, but that seemed like a significant change.

[msftrncs]

Note: with this solution, the while check still occurs in a capture if the capture is at the start of the line, in some wild cases that could still cause a problem.

I cannot really figure out what is going on in the failure of the CI. The test script is failing during the markdown part of the tests, but from what I can see of the markdown tests, there is nowhere that this change would have affected. Maybe I am not looking at the right tests?

[msftrncs]

@alexandrudima, any input on this? I did an experiment to find another solution:

	const noRulesOnStack = stack.getRule(grammar) instanceof IncludeOnlyRule;

and then use !noRulesOnStack instead of linePos == 0 to perform the while rules check. Also seems to work, prevents the while rules from running if the capture is at the beginning of a line, but it is probably more expensive.

[alexdima]

Thank you!