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/queries/t_raises_with_invalid_prepared_statement.nim

@@ -0,0 +1,20 @@
+# vim: set et sta sw=4 ts=4 :
+
+import
+    std/re
+import kuzu
+
+let db = newKuzuDatabase()
+let conn = db.connect
+
+var q = conn.query( "CREATE NODE TABLE Doop ( id SERIAL, thing STRING, PRIMARY KEY(id) )" )
+
+var p = conn.prepare( "CREAET (d:Doop {thing: $thing})" )
+assert typeOf( p ) is KuzuPreparedStatement
+
+try:
+    discard p.execute
+except KuzuQueryException as err:
+    assert err.msg.contains( re""".*Error executing prepared statement:.*CREAET""" )
+
+