Give a preference to left-right reading, i.e <postcode>,<address>
prefers a postcode search while <address>,<postcode> rather does
an address search.
Also exclude non-addressables, countries and state from results when a
postcode is contained in the query.
Search is now split into three functions: for free-text search,
for structured search and for search by category. Note that the
free-text search does not have as many hidden features like
coordinate search. Use the search parameters for that.
The implementation follows for most part the PHP code but introduces an
additional layer parameter with which the kind of places to be returned
can be restricted. This replaces the hard-coded exclusion lists.
