Made build.py work again

build.py was unchanged from the S&K disasm. In hope of making this
disasm more multiplatform-accessible, I've made it compatible with this.

I've tested this on Windows 7 running Python 2.7.8; Python 3 is
incompatible (even back in S&K).

Currently, checksum calculations are Windows only (an exe is used).

OSX's build tools do not include the new s1p2bin, though source is
available for those who want to build for other platforms.