Support a variety of connection strategies and backoff when connecting to domain names

[mattrm456]

This PR adds several features to support more robust procedure when initiating connections and handling their failures. First, this PR adds a new class, ntsa::Backoff, that represents either an arithmetic or geometric backoff to a progression of a time interval. Second, a optional ntsa::Backoff policy is supported in the scheduling of a periodic ntci::Timer by specification of the backoff in the associated ntca::TimerOptions used to create the timer. Third, an optional ntsa::Backoff policy can also be indicated in the ntca::ConnectOptions specified when initiating a new asynchronous connect operation of an ntci::StreamSocket. Finally, this PR adds a new ntca::ConnectStrategy enumeration, which allows the user to indicate how the resolution of a domain name should be handled when connecting an ntci::StreamSocket to a domain name: either "resolve the domain name and pick first address supplied by resolution process, an re-resolve after each connection failure" (the current default, and previous behavior), or "resolve the domain name and try each address to which that name resolves before re-resolving" (the new supported behavior.) The connection strategy is indicated in the ntca::ConnectOptions specified when initiating an asynchronous connect operation on an ntci::StreamSocket.