add editorconfig file to unify coding style

  [EditorConfig](http://editorconfig.org/) is a means to help developers keep a consistent coding
  style across IDEs/editors. This way we can all  speak and edit in the same way.

  @bluesmoon If theres not everything you require for your work on boomerang please tell me
  and I'll append it. 
we use smart tab indents, ie, tabs for most lines, with tabs + spaces to align variable names on multiple lines after a single `var` statement.