EP128: Merge my Xep128 into my Xemu project

[lgblgblgb]

Project https://github.com/lgblgblgb/xep128/ with this task: https://github.com/lgblgblgb/xep128/issues/48

Description: Xemu has a primitive framework for my (multiple number of) emulators. It more or less duplicates many parts of Xep128, including emulated hardware parts (like Z80, with the help of a modified Z80ex) and common infrastructure (SDL layer, snapshot handling, OSD, file handling, build mechanism, etc etc, and even more will come, like OSD implemented host OS independent menu system and more) too. Since it's hard to maintain too projects with many common stuff but slightly different implementation, the best would be to merge Xep128 as an emulation target of Xemu project. It would help my EP128 emulator to become even better, also helps Xemu project to be more mature, since it's possible there should be modifications and developments on the Xemu side as well to be able to serve the needs of EP128 emulation, which is more complex than any other emulations in Xemu currently. And also it help me, to maintain less projects and code. :)

[lgblgblgb]

Merged, though many things is done on its own still, only the Z80 emu part and build system which is common. Many things from Xep128 can be useful for other targets too, even currently (separated timing code suitable for all architectures, OSD stuffs, some of the build stuff not used currently within Xemu, etc) or in the future (ie: native file chooser for win and linux, TODO for OSX though).