title: Add data type from PostgreSQL extension in Slick
body: <p>I'm using the PostGIS extension for PostgreSQL and I'm trying to retrieve a <code>PGgeometry</code> object from a table.</p>
  
  <p>This version is working fine :</p>
  
  <pre class="lang-scala prettyprint-override"><code>import java.sql.DriverManager
  import java.sql.Connection
  import org.postgis.PGgeometry
  
  object PostgersqlTest extends App {
    val driver = "org.postgresql.Driver"
    val url = "jdbc:postgresql://localhost:5432/gis"
  
    var connection:Connection = null
  
    try {
      Class.forName(driver)
      connection = DriverManager.getConnection(url)
  
      val statement = connection.createStatement()
      val resultSet = statement.executeQuery("SELECT geom FROM table;")
  
      while ( resultSet.next() ) {
        val geom = resultSet.getObject("geom").asInstanceOf[PGgeometry]
        println(geom)
      }
    } catch {
      case e: Exception =&gt; e.printStackTrace()
    }
    connection.close()
  }
  </code></pre>
  
  <p>I need to be able to do the same thing using Slick custom query. But this version doesn't work :</p>
  
  <pre class="lang-scala prettyprint-override"><code>Q.queryNA[PGgeometry]("SELECT geom FROM table;")
  </code></pre>
  
  <p>and gives me this compilation error</p>
  
  <pre><code>Error:(50, 40) could not find implicit value for parameter rconv: scala.slick.jdbc.GetResult[org.postgis.PGgeometry]
    val query = Q.queryNA[PGgeometry](
                                     ^
  </code></pre>
  
  <p>Is there a simple way to add the <code>PGgeometry</code> data type in Slick without having to convert the returned object to a String and parse it?</p>