code: public void add(final long version) {
          versionWindow[versionWriteHead++] = version;
          if (versionWriteHead == versionWindow.length) {
              versionWriteHead = 0;
          }
          versionsStored++;
      }
docs: Add a new block version to the tally, and return the count for that version
  within the window.
  
  @param version the block version to add.