Added .editorconfig to tell others about spaces and tabs

Also:
- formated source code according to these rules;
- added spaces after commas in test code

See GitHub issue #101

.editorconfig

@@ -0,0 +1,15 @@
+# @see http://editorconfig.org/
+
+# This is the top-most .editorconfig file; do not search in parent directories.
+root = true
+
+# All files.
+[*]
+indent_style = space
+indent_size = 4
+charset = utf-8
+trim_trailing_whitespace = true
+insert_final_newline = true
+
+[composer.json]
+indent_size = 4