Allow a type parameter for the row results

[ayrton]

Accept a type parameter for the execute function that represents the returned results. This should allow you to use any of these styles:

// 1. use default row type `type Row = Record<string, any>`
const got = await connection.execute('SELECT 1, null from dual;')

// 2. use default row type `type Row = Record<string, any>` and cast
type Row = {
      ':vtg1'?: number
      null?: null
}
const got: ExecutedQuery<Row> = await connection.execute('SELECT 1, null from dual;')

// 3. use your own row type
type Row = {
      ':vtg1'?: number
      null?: null
}
const got = await connection.execute<Row>('SELECT 1, null from dual;')

It uses function overloading to differentiate between rows as object and rows as array.

Fixes #150
Fixes #71

[iheanyi]

I believe we still want to keep this because we want to limit the number of valid options passed into Execute.

[ayrton]

You can only pass these options:

{ as?: 'object'; cast?: Cast } | { as: 'array'; cast?: Cast }

Anything else Typescript will complain:

    261     const got = await connection.execute('SELECT 1 from dual;', null, { as: 'RANDOM' })
                                                                                ~~

      dist/index.d.ts:95:9
        95         as?: 'object';
                   ~~
        The expected type comes from property 'as' which is declared here on type '{ as?: "object"; cast?: (field: Field, value: string) => any; }'
      dist/index.d.ts:99:9
        99         as: 'array';
                   ~~
        The expected type comes from property 'as' which is declared here on type '{ as: "array"; cast?: (field: Field, value: string) => any; }'