fix #711

[JoshKeegan]

See #711

[JoshKeegan]

I've added a couple more fixes (of the same problem for other params) found by searching the solution for "%.
I opted for putting the comma in the string and letting it be URL encoded in StringExtensions.AddParameterToQuery as I thought it was clearer and made this less likely to happen again.

I've left it as-is in TweetQueryGenerator.GetTweetsQuery because the parameter is added in String.Format, so using %2C there saves an explicit URL encoding call, so it does seem cleaner there. I've added a comment just to make it clear what's happenning.

[linvi]

Thanks again :)