Add EditorConfig to force tabs for whitespace

[RobLoach]

I found there was some inconsistent whitespace usage across the files. Adding a EditorConfig definition file, and using the editorconfig extension in your favourite IDE, will ensure all whitespace takes on the same format. In this case, it'll apply tabs across files automatically for you.

[RandyGaul]

Thanks for the idea! I'm a bit picky about whitespace though, so, I'll pass on this one. Really appreciate the PR though! And thanks for putting up your others PRs too, they were very helpful.