In examples, use gmail-britta from the local checkout

This allows us to modify the local tree and run examples on that - too
beautiful for words.
Fix issue #4: incorrect parens when nesting AND in OR

Recursing down into emit_filter_spec should pass the "should emit
parens" knowledge along as well. (Speaking of, this function needs way
better test coverage.)
Version bump to 0.1.6
Regenerate gemspec for version 0.1.6
Allow more recent versions of rake and bundler, Gemfile.lock updated automatically.
Merge pull request #7 from ryansb/bugfix-gemfile

Allow more recent versions of rake and bundler