@js helper

related to https://github.com/linkedin/dustjs-helpers/issues/74

possible extensions to Dust core (which would of course change Dust far from logic-less):
* create functions from expressions to compiled version of template (performance improvement and easy debugging}
* add special Dust language element to eliminate need to wrap expressions to quotes ```{!if people.size()>10}many{:else}acceptable{/if}``` or ```{! "{" + moment(today).format('dd.MM.YYYY') + "}" }```