feat(ci): prebuild the package for easier cross platform use

[inkedsquid]

What does this PR do ?

This PR adds a long-requested feature: prebuilds of the bindings. The process of building is done for every npm i, which is slow and inefficient. By using prebuildify and node-gyp-build, we can create prebuilds for the most popular platforms/distributions and speed up the process considerably.

Here is a simplified schema to show how it works :

How should this be manually tested?

• Step 1 : Build the package via npm build and pack it with NPM.
• Step 2 : Refer to it in a dependent package.
• Step 3 : Launch any desired program using it.
• Step 4 : Check boost-geospatial-index in the node_modules folder. No build folder should be present. If present, it means node-gyp-build was not able to find a compatible prebuild.

Other changes

Adapted the package.json to only pack necessary files.