[Do not merge] Fix lint errors

Opening a new PR to discuss the changes necessary to fix linting errors currently present in the codebase.

This is based on branch created for #280 - please merge that one first before merging this. :)

Currently, there are 92 linting errors, out of which 90 are too long lines (>80). If we would set the maximum line length to 100, we would reduce them to just 13 and setting it to 120 to only 2. What do we do? Do we keep the limit on 80 or shall we increase it?

Another error is creating functions within a loop in [lib/generator.js](https://github.com/google/google-api-nodejs-client/blob/master/lib/generator.js#L164). I was thinking if we could somehow refactor the function so that it's defined only once?

Thanks for feedback!