SQLite SELECT parameters

[russellhaering]

Experimenting with SQLite and this query wasn't working as intended:

/* name: GetUser :one */
SELECT * FROM users WHERE id = ? LIMIT 1;

This PR adds some code to pass WHERE clauses on SELECT statements through to the internal AST, which seems to resolve the issue - although is no means comprehensive (for example sqlc.arg() still does not work).

[russellhaering]

Closing this out. #1687 generates identical code, and handles many more use-cases.