Lif3 L3USD

Contract L3USD takes a less than 0.2% fee for each token transfer, and the fee is collected by the contract owner. If the fees is not flowed back to the users in some way, eventually all the L3USD token would end up in the contract owner's wallet.

The following 2 functions changes important state variables but don't emit relevant events as notifications. 1. Function `transferOwnership()` updates contract owner address. 2. Function `transferFrom()` updates the allowance before token transfer.

The `_to` or `_spender` input address in function `approve()`, `transfer()` and `transferFrom()` are missing a check that it is not `address(0)`. This would allow users to send token to zero address and essentially burn their tokens and decrease the amount of L3USD in circulation.

The variables `name`, `symbol` and `decimals` assigned in the constructor can be declared as `Immutable`. Immutable state variables can be assigned during contract creation, but will remain constant throughout the lifetime of a deployed contract. An advantage of immutable variables is that reading them is significantly cheaper than reading from regular state variables since they are not located in storage.