Simplify page navigation

[henrikfroehling]

As seen in #156 the current workflow for page navigation looks like this:

var pagedParameters = new TraktPagedParameters(1, 10); // page = 1, items per page = 10
TraktPagedResponse<ITraktTrendingShow> trendingShowsResponse = await client.Shows.GetTrendingShowsAsync(null, pagedParameters);

// getting the next page
pagedParameters.Page = pagedParameters.Page + 1;
trendingShowsResponse = await client.Shows.GetTrendingShowsAsync(extendedInfo, pagedParameters);

It would be nice to simply call something like this to get the next page:

while (trendingShowsResponse.HasNextPage)
{
    trendingShowsResponse = await trendingShowsResponse.GetNextPageAsync();
}