Merge pull request #15 from gyst/diazofix

work around bizarro Diazo encoding bug
Update HISTORY.txt
Whitespaces cleanup
housekeeping
Implement ``renderForValue`` on ``ContentTreeBase`` in order to make single valued relation fields work.
resolve
Merge pull request #17 from plone/rnixx_single_valued_relation_field

Rnixx single valued relation field