Merge pull request bavix#88 from bavix/cashier

Add support Cashier

fix mantissa bavix#85, v3.1.5

Merge pull request bavix#79 from bavix/relations

bavix#78 Relations

changelog, add link 3.1.3

### Added

- Allow to free buy with a negative balance
- Add parameter `$allowZero` to method `canWithdraw`

### Fixed
- method canWithdraw, with a negative price, almost always true

add suggest to composer.json

Merge pull request bavix#51 from bavix/3.1

Exchangeable

Merge pull request bavix#59 from bavix/pg11

fix pg11

Fixed creating a wallet with default slug. # 57 @kak2z7702

Update changelog.md