Fixed bug where temp dir wasn't cleaned up on exit.

I can't believe I made this mistake again. Third module running.
Removed debug print().
Merge branch 'optimisation'
Fix for UTF-8 worksheet names.
Added docs for memory optimisation mode.
Updated memory optimisation docs.
Prep for release 0.2.4
Added tmpdir workbook option.
Added 1904 date option.
Moved table_count to worksheet metadata class.
Added docs for tmpdir and date_1904 constructor options.
Prep for release 0.2.5
Renamed sheet_views test case to allow other similar tests.
Added split and freeze pane support.
Added docs for set_selection(), freeze_panes(), and split_panes().
Prep for release 0.2.6
Cleaned up panes example.
Fixed some typos in docs.
Allow keyword args to be passed through cell decorators.
Added default_row() method, tests and example.