Add changelog

changelog/contracts.md

@@ -2,6 +2,47 @@
 
 All notable changes to the contracts will be documented in this file.
 
+## 2021-14-01
+
+**Version 4** is scheduled for upgrade.
+
+### Added
+
+- Multiple blocks can be committed, proven or executed with one transaction.
+- Rollup block timestamp is added.
+- `ChangePubKey` can be authorized without L1 transaction for smart-contract accounts that can be deployed using CREATE2
+  function with specific salt.
+- Block processing is split into three parts: commit, proving onchain, execution. Block is finalized when its executed.
+- Governance now can pause deposits of some tokens.
+- New events `Deposit(token, amount)`, `Withdrawal(token, amount)` are added when funds are deposited or removed from
+  the contract.
+
+### Changed
+
+- Cost of `Deposit` and `FullExit` for user is reduced significantly.
+- Priority queue storage format is changed for gas cost optimization.
+- Block storage format is changed for gas cost optimization.
+- `ChangePubKey` message that should be signed by ETH private key is changed.
+- Upgrade notice period is increased to 2 weeks.
+- `ChangePubKey` with L2 public key that was authorized onchain can be reset if needed after waiting period of 1 day.
+- Maximum gas limit for ETH and ERC20 token withdrawal from zkSync contract is set to be 100k.
+- Proof of the L2 funds in the exodus mode now can be provided by anyone on behalf of any user.
+- Withdrawal from zkSync contract (funds that are withdrawn from L2 but failed to be pushed out of the zkSync contract)
+  now can be done on behalf of any user.
+- Some of the public variables are made internal.
+- Withdraw from the zkSync contract now should be performed using `withdrawPendingBalance` instead of (`withdrawETH`,
+  `withdrawERC20`).
+- Multiple functions and variables are renamed:
+  1. `fullExit` -> `requestFullExit`
+  1. `exit` -> `performExodus`
+  1. `triggerExodusIfNeeded` -> `activateExodusMode`
+  1. `balanceToWithdraw` -> `pendingBalance`
+
+### Removed
+
+- Pending withdrawal queue is removed, instead we try to execute token transfers when we finalize block.
+- All events for user operations (Deposit, Withdraw, etc.) are removed.
+
 ## 2020-09-04
 
 **Version 3** is released.