createPair(address tokenA, address tokenB): create the pair with tokenA and tokenB
    tokenA: token address
    tokenB: another token address

INIT_CODE_PAIR_HASH: the hash code for generating the pair address(bytes32)
allPairsLength: the length of all pairs(uint)

addLiquidity(address tokenA, address tokenB, uint amountADesired, uint amountBDesired, 
            uint amountAMin, uint amountBMin, address to, uint deadline)
    Add the liquidity to pair which consists of tokenA and tokenB
    tokenA: A token address
    tokenB: B token address
    amountADesired: A token amount added to liquidity
    amountBDesired: B token amount added to liquidity
    amountAMin: minimum amount of token A
    amountBMin: minimum amount of token B
    to: user address to receive Gatoswap LP token
    deadline: running time

addLiquidityETH(address token, uint amountTokenDesired, uint amountTokenMin, uint amountETHMin,
            address to, uint deadline) - payable
    Add the liquidity to pair which consists of navtive coin and token
    token: token address
    amountTokenDesired: token amount added to liquidity
    amountTokenMin: minimum amount of token
    amountETHMin: minimum amount of native coin
    to: user address to receive Gatoswap LP token
    deadline: running time

removeLiquidity(address tokenA, address tokenB, uint liquidity, uint amountAMin, uint amountBMin,
              address to, uint deadline)
    Remove the liquidity from pair which consists of tokenA and tokenB and send the tokenA and tokenB of liquidity.
    tokenA: A token address
    tokenB: B token address
    liquidity: taken liquidity amount
    amountAMin: minimum amount of token A
    amountBMin: minimum amount of token B
    to: user address to receive Gatoswap LP token
    deadline: running time

removeLiquidityETH(address token, uint liquidity, uint amountTokenMin, uint amountETHMin, address to, uint deadline)
    Remove the liquidity from pair which consists of BNB and token
    token: token address
    liquidity: taken liquidity amount
    amountTokenMin: minimum amount of token
    amountETHMin: minimum amount of BNB
    to: user address to receive Gatoswap LP token
    deadline: running time

swapExactTokensForTokens(uint amountIn, uint amountOutMin, address[] calldata path, address to, uint deadline)
    swap the tokenA to tokenB
    amountIn: amount of input token
    amountOutMin: minimum amount of output token
    path: swapping path
    to: user address to receive the tokenB
    deadline: running time

swapExactTokensForTokens(uint amountOut, uint amountInMin, address[] calldata path, address to, uint deadline)
    Swap the tokenB to tokenA
    amountOut: exact amount of output token
    amountInMin: minimum amount of input token
    path: swapping path
    to: user address to receive the tokenB
    deadline: running time

swapExactETHForTokens(uint amountOutMin, address[] calldata path, address to, uint deadline) - payable
    Swap the BNB to token
    amountOutMin: minimum amount of output token
    path: swapping path
    to: user address to receive the tokenB
    deadline: running time

swapTokensForExactETH(uint amountOut, uint amountInMax, address[] calldata path, address to, uint deadline)
    Swap the token to BNB
    amountOut: exact amount of BNB
    amountInMin: minimum amount of input token
    path: swapping path
    to: user address to receive the tokenB
    deadline: running time

swapExactTokensForETH(uint amountIn, uint amountOutMin, address[] calldata path, address to, uint deadline)
    Swap the token to BNB
    amountIn: exact amount of token
    amountOutMin: minimum amount of output BNB
    path: swapping path
    to: user address to receive the tokenB
    deadline: running time

swapETHForExactTokens(uint amountOut, address[] calldata path, address to, uint deadline) - payable
    Swap the BNB to token
    amountOut: exact amount of token
    path: swapping path
    to: user address to receive the tokenB
    deadline: running time

getAmountOut(uint amountIn, uint reserveIn, uint reserveOut)
    Given an input amount of an asset and pair reserves, returns the maximum output amount of the other asset
    amountIn: exact input amount
    reserveIn: reserve amount of input token
    reserveOut: reserve amount of output token
    path: swapping path
getAmountIn(uint amountOut, uint reserveIn, uint reserveOut) 
    Given an output amount of an asset and pair reserves, returns a required input amount of the other asset
    amountOut: exact output amount
    reserveIn: reserve amount of input token
    reserveOut: reserve amount of output token
getAmountsOut(uint amountIn, address[] memory path)
    Performs chained getAmountOut calculations on any number of pairs
    amountIn: exact input amount
    path: swapping path
getAmountsIn(uint amountOut, address[] memory path)
    performs chained getAmountIn calculations on any number of pairs
    amountOut: exact output amount
    path: swapping path