Support for alternative build tools (node-cmake)

In an effort to ditch the python dependency of node-gyp, we've been experimenting with node-cmake, which is a thin wrapper around cmake.

It's use is quite straightforward if you're already using CMake. We just added this:

https://github.com/mapbox/route-annotator/blob/b07d7751988419482b84e536ec84205543466c88/CMakeLists.txt#L44-L62

and we can build our .node binary with:

./node_modules/.bin/ncmake --build

After this is run, all the usual node-pre-gyp package, node-pre-gyp publish commands work as expected.

With a little bit of hackery, I added support for ncmake to node-pre-gyp build by providing an alternative to lib/util/compile.js that calls the appropriate ncmake commands instead of their node-gyp equivalents.

Would it make sense to support alternative build tools like this in node-pre-gyp on a larger scale? The publishing logic is well established and independent of the build tool.

An alternative might be to fork node-pre-gyp into node-pre-cmake.

Start by reading lib/util/compile.js and the linked CMakeLists.txt section, then compare the existing node-gyp build path with the ncmake commands described in the issue. Determine whether the requested scope is a general alternative-build-tool interface or support specifically for ncmake; done means the chosen approach builds successfully while preserving the existing packaging and publishing commands.