use assertSame() where appropriate
- make feed URL configurable
- remove Feed::WEATHER_API_URL
- remove Feed::registerXpathNamespace()
- remove Feed::WEATHER_API_XPATH_NAMESPACE
- fix XML namespace related error handling
- make Feed::fetchData() throw \RuntimeException as documented and pass previous Exception to \RuntimeException
- add test feeds for unit tests to avoid external API dependency in tests
use test feeds for all unit tests to avoid external API dependency
update version number to 0.3.0