Add documented but missing count to GetLists()

[M4rtinK]

The GetLists() method documents the count parameter, which is actually not available in the method signature and can't be used.

Due to this, the GetLists() method is basically limited to retrieving ~300 lists at once, as the internally called GetListsPaged() method will retrieve only 20 lists at once and will hit rate limits after 15 calls in a row.

So add "count" to the method signature and pass it to GetListsPaged(). Also add a note about rate limits & hint to bump "count" once they start to be hit.

With this change a caller that passes say 500 as "count" (tested) can retrieve 300+ lists without unnecessarily hitting rate limits.

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This change is 

[M4rtinK]

A couple notes:

• cursor is also documented for GetLists() - should it be also added to the method signature or possibly dropped ?

• We could avoid exposing count in GetLists() and set count for the nested GetListsPaged() to a high value - say 500 or even 900 (Twitter docs say it will never return more than 1000 results). That way rate limits would be avoided automatically for even very high to unrealistic user lists counts (7500-13500).

Please let me know about your preferences & I can change the PR accordingly. :)