initial pass at PARTITION KEY support.

TODO

@@ -0,0 +1,7 @@
+# partition
+
+- UPDATE on partition key values
+  - remove previous row from chunk, insert into new one?
+- enforce column types on insert?
+- allow null values?
+- properly sqlite3_vtab_nochange / sqlite3_value_nochange handling

test.sql

@@ -0,0 +1,49 @@
+.load dist/vec0
+.echo on
+.bail on
+
+.mode qbox
+
+create virtual table v using vec0(a float[1]);
+select count(*) from v_chunks;
+insert into v(a) values ('[1.11]');
+select * from v;
+drop table v;
+
+create virtual table v using vec0(
+
+  v_aaa float[1],
+  partk_xxx int partition key,
+  v_bbb float[2],
+  partk_yyy text partition key,
+  chunk_size=32
+);
+
+
+insert into v(rowid, v_aaa, partk_xxx, v_bbb, partk_yyy) values
+  (1, '[.1]', 999, '[.11, .11]', 'alex'),
+  (2, '[.2]', 999, '[.22, .22]', 'alex'),
+  (3, '[.3]', 999, '[.33, .33]', 'brian');
+
+
+select rowid, vec_to_json(v_aaa), partk_xxx, vec_to_json(v_bbb), partk_yyy from v;
+
+select * from v;
+select * from v where rowid = 2;
+update v
+set v_aaa = '[.222]',
+  v_bbb = '[.222, .222]'
+where rowid = 2;
+
+select rowid, vec_to_json(v_aaa), partk_xxx, vec_to_json(v_bbb), partk_yyy from v;
+
+select chunk_id, size, sequence_id, partition00, partition01, (validity), length(rowids) from v_chunks;
+
+--explain query plan
+select *, distance
+from v
+where v_aaa match '[.5]'
+  and partk_xxx = 999
+  and partk_yyy = 'alex'
+  --and partk_xxx != 20
+  and k = 5;