v004

20180825

• dma: rewrite and extract it to VpdDmaHandler
• dma: initial support for DMA transfer rate
• emu: add region override
• ntsc: add support for V30 and H40
• sram: refactor impl
• vdp: do not set hblank on !displayEnable
• vdp: extract memory handling to a separate class
• z80: memory access fixes