NFTBOOKS security record

All of the `NFTBS` tokens are sent to the contract deployer when deploying the contract. This could be a centralization risk, as the deployer can distribute tokens without obtaining the consensus of the community. Due to the privilege of the deployer, it is possible to be maliciously manipulated by hackers if the account of the deployer is compromised.

A sandwich attack may happen when an attacker observes a transaction swapping tokens or adding liquidity without setting restrictions on slippage or minimum output amount. The attacker can manipulate the exchange rate by frontrunning (executing before the target) a transaction to purchase one of the assets and make profits by backrunning (executing after the target) a transaction to sell the asset. The following functions are called without setting restrictions on slippage or minimum output amount, so transactions triggering these functions are vulnerable to sandwich attacks, especially when the input amount is large: - `uniswapV2Router.swapExactTokensForETHSupportingFeeOnTransferTokens()` - `uniswapV2Router.addLiquidityETH()`

The contract `BookContract` inherited from the `NFTBookBase` contract is an ERC721 token, which in general should be distinguishable and the ownership can be easily tracked. However, the books can have several identical copies, especially the E-Books can be easily copied and the ownership is hard to tell.