Merge pull request #171 from daweth/fix-strategy-interface

add shares getter in IStrategy.sol

src/contracts/interfaces/IStrategy.sol

@@ -54,6 +54,12 @@ interface IStrategy {
      */
     function userUnderlying(address user) external returns (uint256);
 
+    /**
+     * @notice convenience function for fetching the current total shares of `user` in this strategy, by
+     * querying the `strategyManager` contract
+     */
+    function shares(address user) external view returns (uint256);
+
      /**
      * @notice Used to convert a number of shares to the equivalent amount of underlying tokens for this strategy.
      * @notice In contrast to `sharesToUnderlying`, this function guarantees no state modifications