
- test out package with MySQL (code is already there)

- more examples

- if database driver not specified through argument or option then
  MySQL is used if RMySQL package is loaded and SQLite is used otherwise.
  This is a bit fragile and it would be better if we could check that
  the MySQL driver had actually been loaded.  Note that currently there
  is no way to check this but if RMySQL and DBI were upgraded to support
  such discovery this feature could be added.

- MySQL supports sign(), var_pop(), variance(), var_samp(), std() and 
  stddev_samp() functions but SQLite does not.

- neither MySQL nor SQLite supports median() or quantile()

