* Add num_readonly_accounts slice
* Impl programs in account_keys
* Emulate current account-loading functionality using program-account_keys (breaks exchange_program_api tests)
* Fix test
* Add temporary exchange faucet id
* Update chacha golden
* Split num_credit_only_accounts into separate fields
* Improve readability
* Move message field constants into Message
* Add MessageHeader struct and fixup comments
* Be able to create bank snapshots
* fix clippy
* load snapshot on start
* regenerate account index from the storage
* Remove rc feature dependency
* cleanup
* save snapshot for slot 0
Added CompiledInstruction::program_id() so that we don't need to pass
around instruction indexes just for Message::program_id().
Also added Message.program_ids() that returns a slice so that we
can move those pubkeys into Message::account_keys.