Added fill placeholders function

[albertdahlin]

I have found this function quite useful for me, maybe it could be useful for others?

Maybe there is a better name for it?

fillPlaceholders
        [ ( "page", "2" )
        , ( "total", "100" )
        ]
        "Page {{ page }} of {{ total }}"

will result in "Page 2 of 100"

[jaapz]

Looks useful to me, especially when working with translated strings. Would be nice to have some tests, though!

[albertdahlin]

I will be happy to write some tests. Are you using the tests in /tests dir? I thought they were all 0.18 but maybe that does not matter?

[jaapz]

Honestly I'm not sure what the status of the tests is currently. I'll have to take a look but I'm short on time.