Add the same .editorconfig as from the Ghost repository (#384)

.editorconfig

@@ -0,0 +1,17 @@
+# http://editorconfig.org
+
+root = true
+
+[*]
+charset = utf-8
+indent_style = space
+indent_size = 4
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespace = true
+
+[*.hbs]
+insert_final_newline = false
+
+[*.md]
+trim_trailing_whitespace = false