Fixes #214

Adding support for advisory locks in #212 broke code generation for the queries that used functions with parameter references. This change restores some of that functionality. The only difference is the name of the field on the parameter struct.

SELECT * FROM company_users WHERE company_slug = $1 AND email = LOWER($2);

used to generate

type Params struct {
    CompanySlug string
    Email string
}

but will now generate

type Params struct {
    CompanySlug string
    Lower string
}

I know that's not ideal, but I thought it would be better to provide a hot fix.