Adds decent support for nullable types
Adds support for time in DateTime and Excel NPOI
Adds new NPOI references 2.0.0-RC
Formats the code
Cleans up the code
Makes ExcelNPOIStorage actually work
Merge pull request #18 from mstaessen/stable

Kudus for Michiel Staessen !!!

Thanks for the contribution to the library
Merge pull request #20 from MarcosMeli/stable

To Master