Fix/use parseddls

[nktks]

Hi.

I fixed this usecase.

cat test.sql
-- CREATE NULL_FILTERED INDEX test ON test(test);
CREATE TABLE test(
  test          STRING(36) NOT NULL,
) PRIMARY KEY(test);

go run main.go generate --from-ddl test.sql
error: syntax error:test.sql:1:49: expected token: CREATE, <ident>, but: <eof>

  1:  -- CREATE NULL_FILTERED INDEX test ON test(test)
                                                      ^

exit status 1

This error is caused that yo parse multiple ddls in schema string by using strings.Split(string(b), ";") .
If schema string include comment with semicolon such as-- .*; ,
parse will fail.

So I change to use ParseDDLs on memefish.
This can skip comment collectly.
And I fixed some failed test.

I agreed CLA.
https://cla.developers.google.com/

[kazegusuri]

Ah I see. Looks good!! Sorry for late.

[nktks]

thx!