Support new field 'par_balanced_copied_bytes' of EVENT_GC_STATS_GHC

[duog]

This field was added in this commit.

I would like to add support for this to ghc-events, if you could provide some guidance on how you would like this done.

The options I see are:

• add a Maybe Int to the GCStatsGC constructor
• Add a GCStatsGC data type, with two constructors (perhaps GCStatsGC_V1, GCStatsGC_V2?) where the second has an additional field. This is my preference.

I would also like to add a function

--| Computes the cumulative parallel work balance of the argument garbage collections.   
workBalance :: [GCStatsGC] -> Double

[maoe]

Do you mean GCStatsGHC rather than GCStatsGC?

As to which option to choose, I guess it's a good idea to try both in the threadscope code base to see which one is better to work with.

[duog]

Yes I do mean GCStatsGHC. I'll try both with threadscope as you suggest. It might be a week or two before I get to this.