add value16, value32, value64 datapoints to counter

Alternative solution for wrapping counters. The datapoints value16, value32, value64 are supported by regular counters, but don't show up in the default list of datapoints.

```erlang
17:00:31.573 [info] Application exometer started on node nonode@nohost
2> exometer:new([c], counter, []).
ok
3> exometer:update([c], 4294967290).
ok
4> [begin exometer:update([c], 1), exometer:get_value([c], value32) end || _ <- lists:seq(1,10)].
[{ok,[{value,4294967291}]},
 {ok,[{value,4294967292}]},
 {ok,[{value,4294967293}]},
 {ok,[{value,4294967294}]},
 {ok,[{value,0}]},
 {ok,[{value,1}]},
 {ok,[{value,2}]},
 {ok,[{value,3}]},
 {ok,[{value,4}]},
 {ok,[{value,5}]}]
```