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

src/kuzu/types.nim

@@ -2,19 +2,19 @@
 
 type
     KuzuDatabaseObj = object
-        handle*: kuzu_database
-        path*: string
+        handle:  kuzu_database
+        path*:   string
         config*: kuzu_system_config
         valid = false
     KuzuDatabase* = ref KuzuDatabaseObj
 
     KuzuConnectionObj = object
-        handle*: kuzu_connection
+        handle: kuzu_connection
         valid = false
     KuzuConnection* = ref KuzuConnectionObj
 
     KuzuQueryResultObj = object
-        handle*:         kuzu_query_result
+        handle:          kuzu_query_result
         summary:         kuzu_query_summary
         num_columns*:    uint64 = 0
         num_tuples*:     uint64 = 0
@@ -23,18 +23,24 @@ type
         valid = false
     KuzuQueryResult* = ref KuzuQueryResultObj
 
+    KuzuPreparedStatementObj = object
+        handle: kuzu_prepared_statement
+        conn:   KuzuConnection
+        valid = false
+    KuzuPreparedStatement* = ref KuzuPreparedStatementObj
+
     KuzuFlatTupleObj = object
-        handle*:     kuzu_flat_tuple
+        handle:      kuzu_flat_tuple
         num_columns: uint64 = 0
         valid = false
     KuzuFlatTuple* = ref KuzuFlatTupleObj
 
     KuzuValueObj = object
-        handle*: kuzu_value
+        handle: kuzu_value
         valid = false
     KuzuValue* = ref KuzuValueObj
 
-    KuzuException* = object of CatchableError
+    KuzuException*      = object of CatchableError
     KuzuQueryException* = object of KuzuException
     KuzuIndexException* = object of KuzuException