Rubocop fixes

## Changes
- Fix the majority of rubocop's issues with the code, especially those that are syntax-related.
  - Uses some features that are only supported in Ruby 1.9+, but this shouldn't be an issue as of homesick 1.0.0.
- Ignore the rest of the issues in a new `.rubocop.yml` config file (with comments).
  - Makes it easier to run `rake` when developing other parts of homesick, as the only rubocop issues that would appear would be new.
  - Be sure to un-ignore issues when refactoring, as some of the ignored issues help point out code that is hard to maintain.

## [Results](https://gist.github.com/thenickperson/7b83b993b14ca86e4265)