Addresses #140 by adding duckdb

Next I'll see what test changes are needed to make this fully supported.

src/next/jdbc.clj

@@ -106,6 +106,7 @@
   Database types supported (for `:dbtype`), and their defaults:
   * `derby` -- `org.apache.derby.jdbc.EmbeddedDriver` -- also pass `:create true`
       if you want the database to be automatically created
+  * `duckdb` -- `org.duckdb.DuckDBDriver` -- embedded database
   * `h2` -- `org.h2.Driver` -- for an on-disk database
   * `h2:mem` -- `org.h2.Driver` -- for an in-memory database
   * `hsqldb`, `hsql` -- `org.hsqldb.jdbcDriver`

src/next/jdbc/connection.clj

@@ -67,6 +67,8 @@
   has changed over time (such as with MySQL)."
   {"derby"           {:classname "org.apache.derby.jdbc.EmbeddedDriver"
                       :host :none}
+   "duckdb"          {:classname "org.duckdb.DuckDBDriver"
+                      :host :none}
    "h2"              {:classname "org.h2.Driver"
                       :host :none}
    "h2:mem"          {:classname "org.h2.Driver"}