Better Solr AltParser quoting (closes #730)

Previously the Solr AltParser implementation embedded the search term as an
attribte inside the {!…} construct, which required it to be doubly escaped.

This change contributed by @ivirabyan moves the value outside the query,
requiring only our normal quoting:

    q=(_query_:"{!edismax}Assassin's Creed")

instead of:

    q=(_query_:"{!edismax v='Assassin's Creed'}")

Thanks @ivirabyan for the patch!