improved sorting for addresses with matching postcode

[missinglink]

I was alerted to this issue when investigating an issue of poor locality matching in Australia:

/v1/search?text=22 HENSON STREET, NSW, 2204

1) 22 Henson Street, Brighton-le-Sands, NSW, Australia
2) 22 Henson Street, Dulwich Hill, NSW, Australia
3) 22 Henson Street, Summer Hill (Ashfield), NSW, Australia
4) 22A Henson Street, Summer Hill (Ashfield), NSW, Australia
5) 22 Henson Street, Guildford, NSW, Australia

The issue is that the user supplied a postcode 2204 which was parsed correctly and matched record number 2.

If record 2. matched on the postcode, it should really be scored as no. 1

The reason for this is that the address_search_using_ids query doesn't include any boosting for postalcode matches.

This PR adds an extra query clause for address queries which prioritises addresses with a matching postcode over others, so they sort higher.

/v1/search?text=233 ne 3rd ave, 97124

# before
1) 233 NE 3rd Ave, Canby, OR, USA (97013)
2) 233 NE 3rd Ave, Hillsboro, OR, USA (97124)

# after
1) 233 NE 3rd Ave, Hillsboro, OR, USA (97124)
2) 233 NE 3rd Ave, Canby, OR, USA (97013)

[orangejulius]

Looks good, and this does indeed fix the issue. Acceptance test added