Work on prepared statements.

(Still not working 100%, but getting close.)

Additionally, start on the README, fix some type member visibility, add some
additional tests, tag some FIXMEs for where type conversions will take
place, and add `#rewind` for the query iterator.

FossilOrigin-Name: 490f27a4792d5243d82d90dcb12be1074c945c74d7fa63dd5baaf942ac42d7c9

tests/tuples/t_throws_exception_fetching_at_end.nim

@@ -12,6 +12,6 @@ q = conn.query( "MATCH (d:Doop) RETURN d.thing" )
 
 try:
    discard q.getNext
-except KuzuQueryException as err:
-    assert err.msg.contains( re"""Unable to fetch next tuple.""" )
+except KuzuIndexException as err:
+    assert err.msg.contains( re"""Query iteration past end.""" )