@sdumitriu +1, but I'd make the method more generic:

    String url(Map<String, ?>)

with this behaviour:
* if the value is an array or a collection then iterate and use String.valueOf(Object)
* otherwise use String.valueOf(Object) on the value

This will allow us to write something like:

    $escapetool.url({
        'alice': ['value1', 'value2'],
        'bob': [13, 27]
    })

or

    $escapetool.url({'alice': false, 'bob': $doc.documentReference})

WDYT?