Improve documentation.
Handle struct with no fields in ScanSlice.
Cleanup vet and lint warnings.
fix documentation nits.
Document Do("")
Updated error messages to point to correct variables

Corrected statements for the error messages.
Changed `s.Flush()` to `c.Flush()`.
Changed `s.Recieve()` to `c.Receive()`
Improve ScanStruct, Args.AddFlag documentation.

Note that these functions work on exported fields.