Support market-wide Snapshots and Aggregates

[gcatlin]

Is your feature request related to a problem? Please describe.
A big gap in the market data API is the lack of getting "market wide" snapshot and aggregate data. You can specify a list of symbols, but there's an upper bound per request and you first need to retrieve all Assets. Having market-wide snapshots is needed for scanners / screeners.

Describe the solution you'd like

• Make a single API call to get snapshots for every active symbol today.
• Make a single API call to get daily aggregates for every active symbol for a given date.

Describe alternatives you've considered

• Send multiple requests, covering every symbol in the market (requires retrieving all Assets first)
• Paying for Polygon.io (see here and here)

Additional context

[gcatlin]

That's a fair point. I'll update it to say "multiple" instead of "lots".