Coding style refactor

Refactored the codebase to match a more community-neutral coding style guideline, following [this guide](https://github.com/bbatsov/ruby-style-guide).

Changes include:

  * Indentation from 4 to 2 spaces.
  * One line blocks are now in one line with `{ |x| .. }` instead of `do ... end`
  * One line conditional statements
  * Method calling without `()` whenever possible

Fixes #11.