Revert "remove install section from package.json, and rebuild.js. npm executes binding.gyp automatically. ref https://npmjs.org/doc/json.html"

This reverts commit cfe6e89ac84819a9dcfd5909ab7a8dec173893ff.
Revert "Always rebuild (since bindings are out of date when run through travis)"

This reverts commit dd6fcd0fc4f9416b3e4c97c458eec01a58c3a722.