Updates

[a-frazier]

This is my series of updates to the pre branch.

• Update NuGet Packages to latest versions
• Protect against nulls: Return an empty file if handed a null API result, and add empty rows if there are null objects in a list of objects.
• Only enumerate the API result once: This prevents triggering multiple SQL queries if handed a LINQ to SQL or Entity Framework result.
• Add DateTimeOffsetSupport: All this does is attempt a naive conversion from DateTimeOffset to DateTime, so the resulting value can be serialized into Excel as a DateTime cell instead of a string.