Refactor IO Wrappers

[felixbuenemann]

• Add tests for creating workbooks from path and IOs
• Extract path handling from RubyZip IO wrapper
• Add tests for IO wrappers
• Don't load debug IO wrappers by default

[felixbuenemann]

I removed the following from this PR to be included in the 2.x series:

• Deprecate :io_wrapper option, autodetect wrappers