Enhancements to Unsupported type errors.

[nwstephens]

When users write tables that have columns with unsupported types, they get the message:

Error: Unsupported type

This message would be more useful if error pointed to a specific column:

Error: Column (Species) is of unsupported type

It would also be helpful to tell the user what to do next:

Error: Column of unsupported type. Check that the column types in your R dataframe match the types supported by odbc

We can add documentation to db.rstudio.com that lists supported types here

[jimhester]

Ok, the error message now includes the column name and the type that was not supported.