[Constantinople] Added difficulty bomb delay (EIP1234)

[alextsg]

Fixes #53

[alextsg]

@holgerd77 I'm not sure what's the best way to add tests here, as I don't think difficultyConstantinople.json exists yet on ethereum/tests.

[coveralls]

Coverage increased (+0.5%) to 73.818% when pulling d9de788 on alextsg:eip1234 into dbe2ffb on ethereumjs:master.

[holgerd77]

Hmm, not sure, have asked here: ethereum/tests#318

There is also this spreadsheet with the state of tests, difficulty section seems to be outdated though.

[alextsg]

Thanks @holgerd77. It sounds like tests are coming soon so I'll keep a lookout for that.

[holgerd77]

Difficulty tests for Constantinople are now merged, see new difficultyConstantinople.json file over on the ethereum/tests repo, so we can use this now for testing here in the library.

[holgerd77]

Hi @alextsg, I've now also released a new version v0.6.0 of the ethereumjs-common library including the miner reward parameter changes PR.

[alextsg]

Great, thanks @holgerd77! Will finish this up soon.

[holgerd77]

Hi Alex, if you could update here would be great, then we could finish this part up! 😃

[alextsg]

Sorry about that! Updated

[holgerd77]

Looks good, thanks! 😀