Now that Debug.print() follows the same interface as std.Writer.print(), all the pieces are in place to do some basic print-debugging. This is also a critical step to getting stack traces working for the panic handler; that'll probably be the next major milestone.

I've also started shifting the memory-related functions to a dedicated memory namespace; the existing functions in PI will point there soon, and when I get around to implementing SI that'll be the same deal.

Testing has revealed that @memcpy is good enough for RDRAM and RCP writes, since they're synchronous and since @memcpy seems to be smart enough to write whole words at a time. @memcpy is still unsuitable for PI and SI writes, since it has no means of waiting for previous writes to finish before starting new ones. It's also still risky for RCP writes, since there's no enforcement of write targets starting and ending on word boundaries.