[Ethereum] Is it possible to send/receive Bitcoin using a smart contract

What you probably need is to have a buy and sell functions. A sample could be like:

pragma solidity ^0.4.18;
contract ERC20 {
    function totalSupply() public constant returns (uint);
    function balanceOf(address tokenOwner) public constant returns (uint balance);
    function allowance(address tokenOwner, address spender) public constant returns (uint remaining);
    function transfer(address to, uint tokens) public returns (bool success);
    function approve(address spender, uint tokens) public returns (bool success);
    function transferFrom(address from, address to, uint tokens) public returns (bool success);

    event Transfer(address indexed from, address indexed to, uint tokens);
    event Approval(address indexed tokenOwner, address indexed spender, uint tokens);
}

contract ButAndSell{

    uint public buyPrice = 1;

    function buy(address _tokenAddress) public payable{
        ERC20 token = ERC20(_tokenAddress);
        uint tokens = msg.value * buyPrice;
        require(token.balanceOf(this) >= tokens);
        uint commission = msg.value/100; // 1% of wei tx
       require(address(this).send(commission));
        token.transfer(msg.sender, tokens);
    }
}

Similarly, you can use sell function.

To support multiple tokens you just need to have token balance in your contract. That's all.