Use the correct gem name in Readme

The gem 'flickr-fu' seems to be an old, or completely different version.
To get the actual gem, it has to be 'flickr_fu'.
Merge pull request #20 from skorfmann/master

Use correct gem name in Readme
Merge remote-tracking branch 'upstream/master'
Replace XmlSimple by Nokogiri

- Rewrite most access to use Slop Nokogiri API
- Rewrite 1 test to be compliant with Nokogiri space handling
- Bump version