Clarify RpdePage usage

[nickevansuk]

Clarify usage by naming arguments currentPageAfterTimestamp and currentPageAfterId, to ensure they are not misinterpretted as values from the next page.

OpenActive.NET/OpenActive.NET/rpde/RDPEModels.cs

Lines 164 to 168 in 0def13e

	/// <param name="feedBaseUrl">The base URL of the feed, used to construct the "next" URL.</param>
	/// <param name="afterTimestamp">The afterTimestamp query parameter value of the current request.</param>
	/// <param name="afterId">The afterId query parameter value of the current request.</param>
	/// <param name="items">Items to include in the RPDE Page</param>
	public RpdePage(Uri feedBaseUrl, long? afterTimestamp, ComparableSingleValue<long, string>? afterId, List<RpdeItem> items)