Use more accurate and efficient rootcounter code of PCSX Rearmed in psxcounter.cpp (Cotton and Metal Slug X input is now fixed, no surprise since gamepad updates on PS1 hardware are tied to VBlank rootcounter)
Because VBlank rootcounter is no longer called every HSYNC, sound update is done in psxBranchTest() in r3000a.cpp
Some modifications to SIO code based on PCSX Rearmed (SIO IRQ, sio_cycles value)
Clarified SPU callback function names in plugins.cpp, clarified comments.
Added audio buffer debugging statistics to spu_pcsxrearmed SDL backend.