Add EditorConfig configuration

EditorConfig is a cross plattform/editor plugin to help enforce a
coherent coding style (i.e. line endings, no trailing whitespace,
indentation etc) and supports a load of editors/ides.
See http://editorconfig.org/#download for your the plugins.

For now I set the encoding to utf-8, linux style line endings,
indentation of 2 spaces, insertion of final newline and enabled the
trimming of trailing whitespace.