FR: make new dbOption for use.label

[pgramme]

Hello

As mentioned in #61 and #74, some drivers don't respect JDBC specs about column names vs column labels. The fix you proposed and implemented works fine! (tested for Sas) However, as a user, it is annoying to repeat the parameter at each call to dbFetch/dbGetQuery.

Would you agree to make a new dbOption (e.g. "fetch.use.label") to control the default value per driver or per connection?

I think it only requires modifying the 2 following lines, in dbGetQuery and fetch, and documenting.

I'm happy to propose a PR if it helps

Thanks
Pierre

[pgramme]

Related issue by the way: in function JDBC(), options=opts should be passed down to the new("JDBCDriver", ...) call in all of the 3 cases. Currently only done in first case