GXemul Code2

Renaming oldtestmips back to testmips.

Removing the MIPS CPU emulation and testmips machines from the new framework completely. Any MIPS enhancements and bug fixes will go into the old framework only.

De-emphasizing the new framework in the man page and in the help/usage message produced when running gxemul with no arguments, focusing on the old/legacy framework.

Adding RISC-V 64 instructions.

Moving down some stuff about the New framework in the man page.

Minor update.

Only warn about unimplemented c for Valid entries.

Making the short-list of the TODO nicer.

Unfortunately, to make everything work with all guest OSes with many different kinds of CPUs (R3000, R4000, R10000), the invalidation is now O(n) again, but it works.

Update about the cache vaddr fix.