Add API to sqlite3_serialize/deserialize and sqlite3_backup_*

See merge request cznic/sqlite!56

=== RUN   TestIssue152
=== RUN   TestIssue152/SELECT_1_WHERE_false
=== RUN   TestIssue152/--_just_a_comment
    all_test.go:3019: sql: no Rows available
--- FAIL: TestIssue152 (0.00s)
    --- PASS: TestIssue152/SELECT_1_WHERE_false (0.00s)
    --- FAIL: TestIssue152/--_just_a_comment (0.00s)
panic: runtime error: invalid memory address or nil pointer dereference [recovered]
	panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x18 pc=0x5b5c69]

goroutine 9 [running]:
testing.tRunner.func1.2({0xaeff40, 0x13d9870})
	/usr/local/go/src/testing/testing.go:1526 +0x24e
testing.tRunner.func1()
	/usr/local/go/src/testing/testing.go:1529 +0x39f
panic({0xaeff40, 0x13d9870})
	/usr/local/go/src/runtime/panic.go:884 +0x213
database/sql.(*Rows).close.func1()
	/usr/local/go/src/database/sql/sql.go:3287 +0x29
database/sql.withLock({0xf82190, 0xc0001be990}, 0xc0001fbca0)
	/usr/local/go/src/database/sql/sql.go:3405 +0x8c
database/sql.(*Rows).close(0xc000133480, {0x0, 0x0})
	/usr/local/go/src/database/sql/sql.go:3286 +0x16d
database/sql.(*Rows).Close(0x4f12c6?)
	/usr/local/go/src/database/sql/sql.go:3270 +0x1d
runtime.Goexit()
	/usr/local/go/src/runtime/panic.go:522 +0x177
testing.(*common).FailNow(0xc000135040)
	/usr/local/go/src/testing/testing.go:980 +0x4c
testing.(*common).Fatal(0xc000135040, {0xc0001fbf18?, 0xc00001a0f0?, 0xb34fee?})
	/usr/local/go/src/testing/testing.go:1057 +0x58
modernc.org/sqlite.testIssue152(0xc000135040, {0xb34fee, 0x11})
	/home/jnml/src/modernc.org/sqlite/all_test.go:3019 +0x1d0
modernc.org/sqlite.TestIssue152.func1(0x0?)
	/home/jnml/src/modernc.org/sqlite/all_test.go:2998 +0x25
testing.tRunner(0xc000135040, 0xc0000638a0)
	/usr/local/go/src/testing/testing.go:1576 +0x10b
created by testing.(*T).Run
	/usr/local/go/src/testing/testing.go:1629 +0x3ea
exit status 2
FAIL	modernc.org/sqlite	0.008s

test binary compiled for linux/amd64
=== RUN   TestIssue153
=== RUN   TestIssue153/SELECT_1_WHERE_false
=== RUN   TestIssue153/--_just_a_comment
=== RUN   TestIssue153/#00
--- PASS: TestIssue153 (0.00s)
    --- PASS: TestIssue153/SELECT_1_WHERE_false (0.00s)
    --- PASS: TestIssue153/--_just_a_comment (0.00s)
    --- PASS: TestIssue153/#00 (0.00s)
PASS
ok  	modernc.org/sqlite	0.029s

From the issue:

> This issue might be related to this one: #152 (closed)

Confirmed.

Previously ColumnTypeScanType returned the reflect.Type of [][]byte
for BLOB columns, resulting in a failure to scan when the type was
constructed dynamically based on this return.