Rename AutoIncrementing to Counter (#1307)

contracts/utils/Counter.sol

@@ -2,28 +2,28 @@ pragma solidity ^0.4.24;
 
 
 /**
- * @title AutoIncrementing
+ * @title Counter
  * @author Matt Condon (@shrugs)
- * @dev Provides an auto-incrementing uint256 id acquired by the `Counter#nextId` getter.
+ * @dev Provides an incrementing uint256 id acquired by the `Index#next` getter.
  * Use this for issuing ERC721 ids or keeping track of request ids, anything you want, really.
  *
- * Include with `using AutoIncrementing for AutoIncrementing.Counter;`
+ * Include with `using Counter for Counter.Index;`
  * @notice Does not allow an Id of 0, which is popularly used to signify a null state in solidity.
  * Does not protect from overflows, but if you have 2^256 ids, you have other problems.
  * (But actually, it's generally impossible to increment a counter this many times, energy wise
  * so it's not something you have to worry about.)
  */
-library AutoIncrementing {
+library Counter {
 
-  struct Counter {
-    uint256 prevId; // default: 0
+  struct Index {
+    uint256 currentId; // default: 0
   }
 
-  function nextId(Counter storage counter)
+  function next(Index storage index)
     internal
     returns (uint256)
   {
-    counter.prevId = counter.prevId + 1;
-    return counter.prevId;
+    index.currentId = index.currentId + 1;
+    return index.currentId;
   }
 }