FC模拟器HalfNES v0.049

FC模拟器，新版更新如下：

HalfNES v0.048 Changelog:
-CPU core is much improved. All undocumented opcodes should now be implemented
and cycle timing is more correct.
-Fixed Low G Man crashing after the first boss
-APU is now synchronized exactly with CPU (lowers performance, but fixes
Dreamworld Pogie)
-Made DMC sample channel timing more accurate, which fixed Bee 52 and several
DPCM letterbox demos and made Fire Hawk at least show the titlescreen/intro.
(Still crashes in game.)
-Made the audio high pass filter more aggressive to eliminate clipping and noise
-Fixed VRC7 audio envelopes (Rate was right but notes couldn't be turned off
while in the decay phase. Now that works.)
-Fixed PPU OAM reading to pass oam_stress test and used blargg's NES power up