由于il2cpp在4.6.3下存在如下bug导致sharpzipLib无法使用：
bug如下：
	byte b = 205;
	Debug.Log( (b & 0xff) << 8) 
	在il2cpp下表达式计算是0
	
修改sharpzipLib源码，规避上述bug
1.StreamManipulator类PeekBits函数修改如下
public int PeekBits(int bitCount)
		{
			if (bitsInBuffer_ < bitCount) {
				if (windowStart_ == windowEnd_) {
					return -1; // ok
				}
                int tmp1 = window_[windowStart_++] & 0xff;
                int tmp2 = window_[windowStart_++] & 0xff;
                buffer_ |= (uint)((tmp1 | tmp2 << 8) << bitsInBuffer_);
				bitsInBuffer_ += 16;
			}
			return (int)(buffer_ & ((1 << bitCount) - 1));
		}
		
2.DeflaterHuffman类BitReverse函数修改如下：
public static short BitReverse(int toReverse) 
		{
            int t1 = bit4Reverse[toReverse & 0xF];
            int t2 = bit4Reverse[(toReverse >> 4) & 0xF];
            int t3 = bit4Reverse[(toReverse >> 8) & 0xF];
            int t4 = bit4Reverse[(toReverse >> 12) & 0xF];
            int t5 = t1 << 12;
            int t6 = t2 << 8;
            int t7 = t3 << 4;
            int t8 = t4 << 0;
			return (short) (t5 | t6 | t7 | t8);
		}