performance improvement (mostly on memory allocation)

[MithrilMan]

I'm working on pushing dotnet core to the limit in terms of performance and memory allocation, and I'mopening issues on NBitcoin when I find something interesting that can be improved, let me link here 2 of these issues that may interest you:

MetacoSA/NBitcoin#793
MetacoSA/NBitcoin#796

the 2nd one gives really a boost over memory allocation, that's a problem that fullnode is experiencing a lot (memory usage and fragmentation)