Initial work on porting optimisation mode.
Initial work on porting optimisation mode.
Initial working set_optimization() mode. For #7.
Merge branch 'optimisation' of github.com:jmcnamara/XlsxWriter into optimisation

Conflicts:
	xlsxwriter/worksheet.py
	xlsxwriter/xmlwriter.py
Fix for missed merge conflict. For #7.

Always run tests after merge.
Always run tests after merge.
Always run tests after merge.
Always run tests after merge.
Always run tests after merge.
Always run tests after merge.
Added docstring for set_optimization().
Added more optimization mode testcasses.
Added support for Unicode in optimization mode.
Made optimization mode a constructor option.
Added performance tests.
Merge branch 'optimisation'