add .editorconfig matching CONTRIBUTING.md specs

.editorconfig

@@ -0,0 +1,24 @@
+# EditorConfig is awesome: http://EditorConfig.org
+
+# top-most EditorConfig file
+root = true
+
+# Unix-style newlines with a newline ending every file
+[*]
+end_of_line = lf
+insert_final_newline = true
+max_line_length = 80
+
+# Tab indentation (no size specified)
+[Makefile]
+indent_style = tab
+
+# Indentation override for all JS under lib directory
+[src/**.js]
+indent_style = space
+indent_size = 2
+
+# Matches the exact files either package.json or .circle.yml
+[{package.json,.circle.yml}]
+indent_style = space
+indent_size = 2