Goodbye, bad whitespace

This commit will remove hard tabs and trailing whitespace from lines throughout the codebase.

In order to reveal offending lines, I used a version of bundler's [quality_spec](https://github.com/bundler/bundler/blob/master/spec/quality_spec.rb).  The spec breaks with more recent versions of rspec, which is the only reason I haven't included the spec itself with this PR.