NAPI conversion

[Eugeny]

Converted the module to NAPI

[sylveon]

What's the benefit of using NAPI? Also, I'm worried that ToNumber().Int64Value() might not always work since IEEE 754 doubles cannot accurately represent all values that a 64-bits pointer/integer can. So if a window handle is bigger than Number.MAX_SAFE_INTEGER, it won't work. Reading 64-bits from a buffer, as electron provides us, will always work.