Add support for Muir Glacier fork

[cburgdorf]

What was wrong?

Muir Glacier is expected to arrive shorty after the dawn of 2020. We aren't prepared yet.

How was it fixed?

1. Upgrade to the next Py-EVM version (which isn't released yet)
2. Configure MuirGlacierVM where the most recent VM is expected.
3. Make Istanbul the minimal supported transaction type

To-Do

• Clean up commit history

• Add entry to the release notes

Cute Animal Picture

[gsalgado]

Looks good to me, but I wonder if there's a checklist of things we need to change in order to add support for a new fork? Would it be worth documenting that?

[veox]

I wonder if there's a checklist of things we need to change in order to add support for a new fork?

@gsalgado I'd guess not, since that's only begun as a draft PR in py-evm. Not in py-evm -> probably not in trinity. Either way, I didn't find anything.

[cburgdorf]

Yeah, I'll make sure to get us documentation to assist with forks in the future.