add tns option for oracle connections
split adapters into separate files
add stream method to adapters

this allows records to be handled sequentially rather than querying the
entire set. note that the event handling for the mssql driver is
synchronous, so this doesn't gain much there yet. will need to look into
how hard it is to defer the next record from being processed
Merge pull request #3 from MattKunze/stream-records

Stream records