Openoffice reading fixes for Nokogiri 1.5.6 changes

[] operator on XML nodes now requires the namespace to be specified
reading of ODS files was broken in roo 1.10.2 + Nokogiri 1.5.6

Signed-off-by: Karsten Richter <kasi@kasi-net.org>
generalized change for nokogiri 1.5.6 to also work in 1.5.5
new helper method "safe_attr" to safely retrieve attributes[].value
or nil if the attr doesn't exist

Signed-off-by: Karsten Richter <kasi@kasi-net.org>
Merge pull request #18 from dc7kr/master

Fixes for ODS reading with nokogiri 1.5.6
Rename OpenOffice#safe_attr -> #attr and tidy up.
Back-fill some history from 1.10.2
Release 1.10.3, with the dependency on nokogiri relaxed to 1.4.0.
Iconv was replaced by String#encode
Be more liberal about how formats are detected.
Use duck-typing to decide whether to extend string.
Use our old Excelx::FORMATS hash to spec out the new implementation. Support some (mildly dubious) exceptions for backwards compatibility.
Delete empty useless roo binary.
Version bump to 0.0.0
Switch from bones to jeweler for easier releases, and do some minor reorganization.
Ignore rbenv's .ruby-version
Add a rake test task to complement jeweler.
Merge remote-tracking branch 'Xaver/master' into releasee

https://github.com/Empact/roo/pull/19
Don't require rubygems or ruby 1.8.
Bump to 1.11.0, requiring ruby 1.9.0+
Declare the MIT license in the gemspec.
fix bundler warning by excluding log file that is being gitignored