Named Format Options Bug Fix

PR #29: fixing custom formats by string

This fixes the option to pass a second argument as a string which represents a named custom formatter:

{{intlNumber NUM "foo"}}
{{intlDate 1390518044403 "bar"}}

It also fixes the message format for something like this:

the cost {price, number, foo} will be ready by {deadline, date, bar}

Where foo is an Intl.NumberFormat options object, and bar is an Intl.DateTimeFormat options object.