Reduce block reward

[cslarson]

This EIP is proposal to reduce the block reward to 1 ETH / block from the present 3 ETH / block at a future, as present unplanned hard fork to be named Perinthos (before Constantinople). The rationale for reducing the block reward stems from the present tremendous growth in hashrate (and corresponding environmental costs) as well as the counter-productiveness of fostering growth in GPU mining.

[pirapira]

Looks good to merge as a draft.

The next step is to figure out the attitudes of client implementors.

[cypheron]

In the last six months hashrate has been going sideways (https://etherscan.io/chart/hashrate). The used argumentation "present tremendous growth" is no longer valid.

[MicahZoltu]

It is not a given that the network hashrate must always increase. It needs to be high enough to secure the system, and no higher. Sometimes this may mean stable hash rate, sometimes a hash rate increase, and sometimes a hash rate decrease.