Initial pass at UPDATE support

[PThorpe92]

This PR is to support Update queries. Follows sqlite behavior as much as possible.

limbo

limbo> create table t (a,b,c);
limbo> explain update t set a = 1 where b = 2;
addr  opcode             p1    p2    p3    p4             p5  comment
----  -----------------  ----  ----  ----  -------------  --  -------
0     Init               0     18    0                    0   Start at 18
1     OpenWriteAsync     0     2     0                    0
2     OpenWriteAwait     0     0     0                    0
3     RewindAsync        0     0     0                    0
4     RewindAwait        0     17    0                    0   Rewind table t
5       Column           0     1     4                    0   r[4]=t.b
6       Ne               4     5     15                   0   if r[4]!=r[5] goto 15
7       RowId            0     6     0                    0   r[6]=t.rowid
8       IsNull           6     17    0                    0   if (r[6]==NULL) goto 17
9       Integer          1     1     0                    0   r[1]=1
10      Column           0     1     2                    0   r[2]=t.b
11      Column           0     2     3                    0   r[3]=t.c
12      MakeRecord       1     3     7                    0   r[7]=mkrec(r[1..3])
13      InsertAsync      0     7     6                    0
14      InsertAwait      0     0     0                    0
15    NextAsync          0     0     0                    0
16    NextAwait          0     5     0                    0
17    Halt               0     0     0                    0
18    Transaction        0     1     0                    0   write=true
19    Integer            2     5     0                    0   r[5]=2
20    Goto               0     1     0                    0

sqlite

sqlite> explain update t set a = 1 where b = 2;
addr  opcode         p1    p2    p3    p4             p5  comment
----  -------------  ----  ----  ----  -------------  --  -------------
0     Init           0     15    0                    0   Start at 15
1     Null           0     1     2                    0   r[1..2]=NULL
2     Noop           1     0     1                    0
3     OpenWrite      0     2     0     2              0   root=2 iDb=0; t
4     Rewind         0     14    0                    0
5       Column         0     1     5                    0   r[5]= cursor 0 column 1
6       Ne             6     13    5     BINARY-8       81  if r[5]!=r[6] goto 13
7       Rowid          0     2     0                    0   r[2]= rowid of 0
8       IsNull         2     14    0                    0   if r[2]==NULL goto 14
9       Integer        1     3     0                    0   r[3]=1
10      Column         0     1     4                    0   r[4]= cursor 0 column 1
11      MakeRecord     3     2     1                    0   r[1]=mkrec(r[3..4])
12      Insert         0     1     2     t              7   intkey=r[2] data=r[1]
13    Next           0     5     0                    1
14    Halt           0     0     0                    0
15    Transaction    0     1     1     0              1   usesStmtJournal=0
16    Integer        2     6     0                    0   r[6]=2
17    Goto           0     1     0                    0

[PThorpe92]

EDIT: nevermind, fixed it. this should be good to go