add editor config

• Add EditorConfig file to allow basic coding style consistency between different IDEs and project members
• See https://editorconfig.org/

For EditorConfig to work please install plugins for the IDEs:

• VScode: https://marketplace.visualstudio.com/items?itemName=EditorConfig.EditorConfig
• Eclipse: https://marketplace.eclipse.org/content/editorconfig-eclipse
• Sublime: https://packagecontrol.io/packages/EditorConfig