Release 0.6.8

• bugfix in HTMLTable.to_csv for Python 3 related to writing non-ascii characters to csv file
• Link to new example added to readme
• session added property index_rev, which now is used to save index in file
• bugfix in utils.AttrDict.__dir__ method. now it works allowing IPython auto-comlete for
  objects that use utils.AttrDict class
• better support of last IPython shell
• prefetching:
  • bugfix: some times when passed few fields with
    same names, prefetch raises strange errors (atleast on odoo 7.0 instance)
  • improvement: prefetch only records that have no atleast one field in cache