* SDK: Add sysvar to expose recent block hashes to programs
* Blockhashes is one word
* Missed one
* Avoid allocs on update
* unwrap_or_else
* Use iterators
* Add microbench
* Revert "unwrap_or_else"
This reverts commit a8f8c3bfbe.
* Revert "Avoid allocs on update"
This reverts commit 486f01790c.
* rename rent.rs to rent_calculator.rs
* add rent sysvar
* integrate rent_calculator with bank
* rent_calculator integration with genesis
* add test for rent sysvar