Implement a lazy gettext / ngettext / etc wrapper.

The translation setup in version 1 worked for gettext and worked as follows:

* ``_ = new jed({})``
* ``_.gettext("Welcome to my app!")`` (this is a noop but marks the text for .pot file generation)
* the state ``.translate(i18n)`` method called ``i18n.gettext(...)`` once the real ``jed`` instance was available.

This works for ``gettext`` but is too dumb for ``ngettext`` and friends which require a proper lazy gettext / ngettext evaluation.