Set up a global .gitignore.

- Create a .gitignore-global file; the contents are inspired by
  https://github.com/github/gitignore/blob/master/Global/OSX.gitignore

- Tell git about the file in .gitconfig.
.vimrc Version 1

- Set nocompatible.
- Configure standard whitespace settings, encoding, etc.
- Put vim-generated files inside ~/.vim directory.
- Use NeoBundle for plugin-management.
- Use vim-sensible plugin.
Set vim as default text-editor for git.