AZIP-4: L1 Block Header Access

[iAmMichaelConnor]

Updates from @joeandrews original proposal.

Temp: a "Cons" section which highlights potential problems with the proposal, to ensure people are comfortable with those problems. This section can be deleted after discussion.

Discussions here: #12

[iAmMichaelConnor]

Copying from @joeandrews in the older thread:

@just-mitch we also need to account for the mana cost of ssz, maybe its negligible but I imagine a lot of use cases will defer the SSZ to a public function to do. Maybe thats a good for fees though :D

[iAmMichaelConnor]

the mana cost of ssz

My understanding is that copying-over the CL root and reading the EL state root from there results in a lag; an older state root than if copying over the EL state root directly. I could be wrong (difficult to figure it out from online info)

[iAmMichaelConnor]

Whoops, discussions here: #12