Merge pull request #108 from baxeico/master

do not catch ValueError exceptions inside method by mistake
easy_install doesn't take "install" parameter
Merge pull request #109 from moogleshoogle2/patch-1

easy_install doesn't take "install" parameter
Minor doc fixes.
Add positioning option to insert_image #117
Merge pull request #119 from mojaie/master

Add positioning option to insert_image #117
Minor fixes.
Made error_bar data optional.

Fix for issue #115.
Prep for relase 0.5.4
Prep for release 0.5.5
Test case for issue #132
Fix for unicode strings in data validation lists.

Fix for issue #135.
Clarify print_area() docs for row/col ranges.

Fix for issue #139.
Made close() a required method call.

Updated the documentation and desctructor exception handler to make
it clear that an implicit close() is required. This is to avoid
confusing errors when an implicit close isn't called by the GC.
Fix for issue #131.
Fix for formula string values. Issue #122.
Prep for release 0.5.6
Minor doc fix.
Fix docs for hide_gridlines().

Closes #129.
Minor doc fix.
Added support for datetime.timedelta.

Issue #128.