Add an .editorconfig file (#632)

Could help to maintain consistent coding styles

What is .editorconfig:
http://editorconfig.org/#overview

Plugins for IDEs to support:
http://editorconfig.org/#download

.editorconfig

@@ -0,0 +1,17 @@
+# http://editorconfig.org
+root = true
+
+[*]
+indent_style = space
+indent_size = 2
+charset = utf-8
+trim_trailing_whitespace = true
+insert_final_newline = true
+max_line_length = 100
+
+# Use 4 spaces for the Python files
+[*.py]
+indent_size = 4
+
+[*.md]
+trim_trailing_whitespace = false