v2.3.0

1. Upgrade Vault to MultiTokenVault for supporting multi-token cash, withdraw and deposit.
2. Change PriceOracle for supporting multi-token storage price set and query.

v2.1.2

1. Limit one node can only deploy one Vault in VaultFactory contract. The officially deployed factory 0x763d7858287B9a33F4bE5bb3df0241dACc59BCc7 will be used to deploy new Vault contracts.
2. Raise error immediately if there is no sufficient balance in a Vault while cashing cheques.
3. Deployed a Vault contract 0x11a91B7270ea000768F7A2C543547e832b5cb031, which servers as an implementation while deploy Vault contracts in UUPS proxy mode.
4. Improve unit tests.

v2.1.0

Changes

1. Issuers can use Vault contract to deposit and withdraw WBTT, which will be used as currency among BTFS nodes. One special Vault address 0x102dbCe01394C4a44Da3a1DF1De418e3fC225077 will server as an implementation contract when deploying vault proxies.
2. VaultProxy contract is a UUPS proxy contract used for deploying Vault, it makes the vault contract upgradeable.
3. VaultFactory is used to deploy multiple vault proxies for different issuers, and its BTTC mainnet address is 0x9AF4bEc1A30BeC47756Ecef4cf43B91592121bC9.
4. PriceOracle contract is used to save the price and exchange rate for BTFS network, and it's address in BTTC mainnet is 0x0064d80C42b6E2cE3aC92eaD445B3D83C510c7AA.