.gitconfig: Add `tags`, `branches` and `remotes` aliases
.gitconfig: Show the diff when writing a commit message

Thanks to @miketaylr: http://twitter.com/miketaylr/status/209688450868326400
.gitconfig: Tweak `ca` alias

Thanks to @necolas! https://github.com/mathiasbynens/dotfiles/commit/15d4c9583d66be40a497706134b637e8c1f10ae6#commitcomment-1416521
.vimrc: Use the OS clipboard by default
Add .hushlogin

The mere presence of this file in the home directory disables the system
copyright notice, the date and time of the last login, the message of the
day as well as other information that may otherwise appear on login.
See `man login`.
.aliases: Add `....` and `.....`
.aliases: Add `h` (`history`) and `j` (`jobs`)
.bash_profile: Add tab completion for many more commands
.vimrc: Explicitly allow the use of backspace in insert mode
.vimrc: Fix typo in comment
.gitignore: Ignore compiled Python files
.hgignore: Initial commit
.bash_profile: Load `.extra` last, allowing it to override any previous settings
.osx: Set language and text formats
.osx: Disable “natural” (Lion-style) scrolling
.osx: Fix typo
.osx: Enable swipe between pages with three fingers

Ref. #80. Thanks to @Lri for the help.
.osx: Group commands in categories
.osx: Minor formatting tweak
.aliases: Update to `stat` v8.17 (GNU coreutils)