Support for Electron 1.4 (V8 5.3.X)

[bengotow]

This PR replaces the get/setHiddenValue APIs with the new V8 Private APIs. I actually wasn't able to find what version introduced them, and I'm not sure if it's important to continue supporting them when Private is not available. Using the private APIs took a few more lines of code, so it might be nice to create a convenience function if both need to be supported.

I also found that node-bindings was unable to resolve the module's root when running in Electron. This line returns undefined: https://github.com/TooTallNate/node-bindings/blob/master/bindings.js#L55.

This PR should resolve #2!

[JoshuaWise]

Thanks for the PR! It is indeed important to support the get/setHiddenValue APIs, since this module needs to continue supporting Node.js 4.x.x and 5.x.x. Some kind of macro will need to get written that detects which version of V8 is being used, and chooses the correct API.

I believe the only way to detect the v8 version is with v8::V8::GetVersion(), which unfortunately returns a const char*, not a number, so some parsing is required. It should be safe to start using the Private API at, and after, version 5.0.71.35.

[bengotow]

Cool sounds good - I'll update the PR!

[JoshuaWise]

It might be a good idea to rebase this branch with a7a6d65, so the changes from #4 (comment) are included.

[JoshuaWise]

I've cleaned up and rewritten much of the ancient history that was in better-sqlite3's git repo. You'll need to re-do your changes after cloning a new repo. I'm sorry about the inconvenience.