Support for delimiter param

[nulldiego]

Add parameter "delimiter"

[mithrandie]

Thank you for creating a pull request, but I'm sorry, I'm not going to merge this request.

When opening this driver, there are three parameters that can be specified in the DNS string: Timezone, DatetimeFormat, AnsiQuotes. These parameters should be specified before parsing queries, and have a slightly different meaning than the other csvq options. For this reason, these can also be set at csvq runtime in the configuration file.

All other options can be specified at any time, so they are not available in the DNS string.

If you want to change the delimiter, you can use the following queries.

1. Use SET FLAG statement.

r := db.QueryRowContext(ctx, "SET @@DELIMITER TO '\t'; SELECT col1, col2 FROM `data.csv`;")

2. Use table function

r := db.QueryRowContext(ctx, "SELECT col1, col2 FROM CSV('\t', `data.csv`")

If you notice anything else, please let me know. Thank you.