Apply latest JEG and add centralised compilation control

[GorgonMeducer]

• Add centralised configuration file jeg_cfg.h
• Add macro option for extern draw pixcel interface
• Add macro option for disabling 6502 bcd mode
• Add macro option for disabling extra 16bit bus read/write
• Add macro option for disabling dma interface
• Apply ppu improvement
• Improve the readablity of ppu_update
• use strncmp to replace original data comparison in cartridge.

[semiversus]

merged your changes and made minor additions. Please have a look,

[GorgonMeducer]

Thank you very much. They are looking good! I'll pull another request soon about PPU improvement for both readability and performance.