Consistency for repo names, core rule names, Readmes, files ...

[CptLausebaer]

I don't know if there is some reason or maybe it is grown historically, but there are some issues with the naming of repos and files among the mednafen/beetle cores.

Example

mednafen-psx-libretro

reponame: mednafen
core rule name: mednafen_psx
readme: beetle
files: both
- https://github.com/libretro/mednafen-psx-libretro/blob/master/beetle_psx_griffin.cpp
- https://github.com/libretro/mednafen-psx-libretro/tree/master/mednafen

---

beetle-bsnes-libretro

reponame: beetle
core rule name: mednafen_snes
readme: madnafen

---

I know it is difficult to change this things, but I think it would improve the structure of the whole libretro project if the cores and the repos have reliable names.