Various fixes and formatting chores (#885)

* fix: clean up solium linting errors

* fix: make various contracts natspec compliant

* fix: this.balance deprecated; convert to address(this).balance

* fix: contract.call deprecated and switch to gasleft()

* fix: ignore empty block rule project-wide

* fix: add ignore cases for the rest of the linting warnings

contracts/ECRecovery.sol

@@ -47,6 +47,7 @@ library ECRecovery {
     if (v != 27 && v != 28) {
       return (address(0));
     } else {
+      // solium-disable-next-line arg-overflow
       return ecrecover(hash, v, r, s);
     }
   }