Use `Brewfile` now that Homebrew supports it

https://github.com/mxcl/homebrew/blob/master/Library/Contributions/cmd/brew-bundle.rb
https://coderwall.com/p/afmnbq
.gitconfig: Make `git rebase` safer on OS X

See <http://www.git-tower.com/blog/make-git-rebase-safe-on-osx/>.

Closes #291.
.aliases: Improve `lsd`

Ref. #292.
README: Use `Brewfile` instead of `.brew`

Closes #294.
.osx: Hide Safari’s sidebar in Top Sites by default

Closes #296.