dbWriteTable s3.location

[DyfanJones]

Appending

When appending to an already exiting table dbWriteTable will just utilize parameter s3.location for S3 location. However an issue will occur if backend data in s3 is situated in a different location i.e.
Backend s3 location: s3://path/to/bucket1/tbl_data/
s3.location parameter: s3://path/to/bucket2/tbl_data/

To over come this the existing s3 location should overwrite s3.location parameter when the parameter append is set to TRUE

Backend S3 structure

Currently data is sent to the s3 path:

s3:/path/to/bucket/{tbl}/

This is ok when user only has 1 database/schema for Athena. When a use has 2 databases i.e:

dbWriteTable(con, "schema1.tbl", tbl)
dbWriteTable(con, "schema12.tbl", tbl)

The back end will return: s3:/path/to/bucket/{tbl}/ for both cases. Ideally it should align to the following schema: s3:/path/to/bucket/{schema}/{tbl}/ and return:

s3:/path/to/bucket/schema1/tbl/
s3:/path/to/bucket/schema2/tbl/

[DyfanJones]

PR #72 fixes issue