[WIP] Fix compilation errors and warnings for Node.js 12.

[benjamn]

Closes #36.

[benjamn]

@jprichardson How committed are you to continuing to support Node 0.12? I ask because that's the only Node version that's still failing. I think I know how to fix it, but the solution would clutter the code with more preprocessor macros.

[pnathan]

It would be cool if this could be merged, or the package taken over. It's been almost half a year.... kexec itself last got updated in 2016. :-/

[jprichardson]

@pnathan tests are failing. Happy for someone to step up and help maintain.

[pnathan]

@jprichardson I'm not a node expert - I'm happy to dedicate some time to fix this in the next few weeks, if you're up for gesturing vaguely at probable directions of error.

[laverdet]

@benjamn nan provides wrappers for the invocations that are failing. If I'm reading the travis error log correctly you would just need to swap out Nan::Get, Nan::Set, and Nan::GetFunction.

[laverdet]

You can also swap out the Utf8Value wrapper with Nan::Utf8String.

[i-am-al-x]

Here is a workaround that uses the Meteor rewrite, "kexec v4.0.0".
https://stackoverflow.com/questions/70884111/fix-kexec-error-failure-problem-broken-that-prevents-unable-to-npm-inst/70884112#70884112
Of course, we would prefer that the rewrite gets pulled into the Master branch, but until then, I documented this workaround, which allowed me to use "npm install" so I could get WebPack working again.