Some improvements to the rules

[dzbarsky]

Hi, just came across this and wanted to mention a few things you might want to look into (I implemented something similar my current company but we haven't open-sourced it)

Headers

• We probably want to grab the node headers from the toolchain vs having a static set. See https://github.com/bazelbuild/rules_nodejs/blob/5af115dac3c59cb69f63a25f745eeceac11b21a2/e2e/smoke/BUILD.bazel#L292 for an example
• The toolchain is currently missing the Windows headers (because I didn't need them) - contributions welcome!

Linking

• I think the OSX linking flags are a little weird; I'm not a linking expert but my understanding is Bazel is trying to move away from those. One of the issues is they're not compatible with fixup chains. See this PR for an example
• I haven't had time to try this yet, but I think the correct solution involves using the new cc_shared_library to control linking, vs the cc_binary + rename hack - which BTW is exactly what I did as well ;)
• I think we'll need the cc_shared_library to depend on the Node/v8 dynamic libs but not link those in, that should give us the behavior we want. Note that this will also require exposing those on the toolchain, which we haven't done yet. A similar change was made to rules_python recently.