Update .gitignore (Add virtualenv files)
Support .vsdx file (fix typo)
Fix could not handle error collectly if visio not found
Update .gitignore (add *.pyc)
Handle an error when broken visio file is given
Do not check file-extensions of visio. Check it on opening (by visio)
Update error messages
Refactoring around filtering pages by --page and --name option.
Refactor around exporting images