Accept tip parameter to return past data

[whoabuddy]

The Stacks Blockchain API supports a tip parameter for read-only contract calls, which can bring up the data at a certain point in time based on the index_block_hash of the Stacks block height.

Ideally we could support specifying the tip as a hash, a block height, or a cycle number.

• tip (hash) could be passed directly
• block height would require a query to get index_tip_hash
• cycle number would require a query to get first-block-in-cycle, then index_tip_hash

The value would be passed as part of the ReadOnlyFunctionOptions, and is accepted by micro-stacks.