Support remaining Geonames services

Five of the webservices listed on that page don't support the XML result format needed by this module.

As of now, the (XML) services that we are missing are:

• astergdem
• cities
• extendedFindNearby
• findNearbyStreets
• findNearByWeather
• findNearestAddress
• findNearestIntersection
• neighbourhood
• ocean

Any new services should be implemented along with a simpletest case.

Added support for "cities" service.

Added "findNearbyStreets" and "findNearestIntersection" services.

Added "findNearestAddress" and "neighbourhood" services.

Added "findNearByWeather" and "ocean" services. Outstanding:

• astergdem
• extendedFindNearby

Added "extendedFindNearby" service.

astergdem doesn't work like the other services, it has result XML like:

    <?xml version="1.0" encoding="UTF-8" standalone="no"?>
    <geonames>
    <astergdem>192</astergdem>
    <lat>50.01</lat>
    <lng>10.2</lng>
    </geonames>

This will need a new method of parsing.

srtm3 has the same problem as astergdem

Disabled astergdem and srtm3 from the configuration, until such time as they actually work.

Added support for custom XML parsers.
Added custom parser for astergdem/srtm3/gtopo30, and configured services to use it.
Re-enable tests for these new services.
Re-enable other tests that were disabled.

The code now supports all 29 XML-based services.

Fixed.