ERC-1967 Proxy Storage Slots

FinalERCcreated 2019-04-246 later proposals build on it

A consistent location where proxies store the address of the logic contract they delegate to, as well as other proxy-specific information.

Authors: Santiago Palladino (@spalladino), Francisco Giordano (@frangio), Hadrien Croubois (@Amxx)

Functions this standard introduces (1)

0x5c60da1b implementation()

Topic0 is the keccak256 hash of the signature, which is what a log filter matches on.

`0xbc7cd75a20ee27fd9adebab32041f755214dbc6bffa90cc0225b39da2e5c2d3b`	`Upgraded(address)`
`0x7e644d79422f17c01e4894b5f4f588d331ebfa28653d42ae832dc59e38c9798f`	`AdminChanged(address,address)`
`0x1cf3b03a6cf19fa2baba4df148e9dcabedea7f8a5c07840e207e5c089be95d3e`	`BeaconUpgraded(address)`

Later proposals that name this one in their requires field.