Add editorconfig file

Trivial config file, which is supported by more or less every editor out
there - either natively or via a plugin.

Should make indentation glitches less common.

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>

.editorconfig

@@ -0,0 +1,13 @@
+# To use this config with your editor, follow the instructions at:
+# http://editorconfig.org
+
+root = true
+
+[*]
+charset = utf-8
+insert_final_newline = true
+indent_style = space
+indent_size = 4
+
+[Makefile]
+indent_style = tab