Pack multiple variables into single EVM storage slot if possible

[franklinsch]

i.e. store four 64-bit integers in a single storage slot

Solidity documentation: https://solidity.readthedocs.io/en/develop/miscellaneous.html#layout-of-state-variables-in-storage

[franklinsch]

YUL has a convenient combineu64tou256 function

[DJRHails]

This will become relevant when we aren't using 256-bits for every type except for Addresses.