adjust sample implementation to match interface

EIPS/eip-7246.md

@@ -84,14 +84,14 @@ interface IERC7246{
      *
      * Emits a {Release} event.
      */
-    function release(address owner, uint amount);
+    function release(address owner, uint amount) external;
 
 
     /**
      * @dev Convenience function for reading the unencumbered balance of an address.
      * Trivially implemented as `balanceOf(owner) - encumberedBalanceOf(owner)`
      */
-    function availableBalanceOf(address owner) external returns (uint);
+    function availableBalanceOf(address owner) public view returns (uint);
 }
 ```
 
@@ -123,7 +123,7 @@ contract EncumberableERC20 is ERC20 {
 
     // The encumbered balance of the token owner. encumberedBalance must not exceed balanceOf for a user
     // Note this means rebasing tokens pose a risk of diminishing and violating this prototocol
-    mapping (address => uint) public encumberedBalance;
+    mapping (address => uint) public encumberedBalanceOf;
     
     address public minter;
 
@@ -140,25 +140,22 @@ contract EncumberableERC20 is ERC20 {
         return true;
     }
 
-    function encumber(address taker, uint amount) public virtual returns (bool) {
+    function encumber(address taker, uint amount) external {
         _encumber(msg.sender, taker, amount);
-        return true;
     }
 
-    function encumberFrom(address owner, address taker, uint amount) public virtual returns (bool) {
+    function encumberFrom(address owner, address taker, uint amount) external {
         require(allowance(owner, msg.sender) >= amount);
        _encumber(owner, taker, amount);
-       return true;
     }
 
-    function release(address owner, uint amount) public virtual returns (bool) {
+    function release(address owner, uint amount) external {
         _release(owner, msg.sender, amount);
-        return true;
     }
 
     // If bringing balance and encumbrances closer to equal, must check
     function availableBalanceOf(address a) public view returns (uint) {
-        return (balanceOf(a) - encumberedBalance[a]);
+        return (balanceOf[a] - encumberedBalanceOf[a]);
     }
 
     function _encumber(address owner, address taker, uint amount) private {
@@ -212,7 +209,7 @@ contract EncumberableERC20 is ERC20 {
         require(currentEncumbrance >= amount, "insufficient encumbrance");
         uint newEncumbrance = currentEncumbrance - amount;
         encumbrances[owner][taker] = newEncumbrance;
-        encumberedBalance[owner] -= amount;
+        encumberedBalanceOf[owner] -= amount;
     }
 }
 ```