Add a .editorconfig

.editorconfig

@@ -0,0 +1,25 @@
+# EditorConfig: http://EditorConfig.org
+
+root = true
+
+[*]
+indent_style = tab
+indent_size = 2
+insert_final_newline = true
+trim_trailing_whitespace = true
+end_of_line = lf
+charset = utf-8
+max_line_length = 79
+
+[{*.html,*.css,*.js}]
+max_line_length = off
+
+[*.py]
+indent_size = 4
+indent_style = space
+
+# Tests don't get a line width restriction.  It's still a good idea to follow
+# the 79 character rule, but in the interests of clarity, tests often need to
+# violate it.
+[**/test_*.py]
+max_line_length = off