Allow users to provide extra paths to bindings

[samuelkubai]

This pull requests allows users of the package to add other paths to the current paths and also avoid having the fileName being undefined. This pull requests allows the users to something like this:

const packageBindings = require("bindings")({
    bindings: "packageName",
    userDefinedTries: [
        ['module_root', 'node_modules', '@sample', 'package', 'build', 'Release',  'bindings'],
    ]
});

This pull request aims to solve the error #50 and add flexibility to the package.