Shortcuts for blank Strings
Revert "Prefer Hash[] over inject({})"

This reverts commit 78e53e391812d9bf4fda3f21d486067f52f100bb.

Reason: the new code creates extra objects
Reduce objects
Avoid unneeded `send` call
String#encode accepts an Encoding
Reduce Strings
Shortcut when given String is UTF-8, which might be the majority case