Added new DMA type which watches for writes to 0x4014 by the CPU and
performs the 256 byte DMA transfer to 0x2004 (OAMData on the PPU).
Added RP2A03.Run which checks for a DMA transfer after each instruction
by calling DMA.PerformDMA.  DMA.PerformDMA will ensure it does return
until the correct number of CPU cycles has elapsed.

Added a simple test for DMA transfers.