EIP-152: Blake2b F precompile (ethereum#2129)

* Brought issue ethereum#152 into the repo as a draft EIP.

Thanks @tjade273!

* Make the draft EIP consistent with the template

Also added myself as an author

* Break backwards compatibility into its own section

* Added notes about the in-progress implementation

Should have a working geth precompile and initial benchmarks shortly

* Specify EIP-2046 as a requirement

While 2046's cheaper precompile contract calls aren't a requirement for
this EIP's implementation, shipping this precompile without EIP-2046
would make the F function expensive for some of the motivating usecases.

* Don't use ABI encoding for precompile

Replace the existing ABI encoding interface to the BLAKE2b `F`
precompile with a loosely pack struct that's `staticcall`-friendly.

H/t to @pdyraga for putting together the interface!

* Add @pdyraga to the EIP authors.

* Remove less relevant EIP rationale

Let's not relitigate precompiles, WASM, etc in thie EIP :)

* Use 0x09 as the precompile address

If a conflicting EIP is moving forward the EIP editor can assign a new
address

* Choosing an EIP number

Contributing docs suggest EIPs be named `eip-draft-with-a-title` until
an editor has been assigned, but discussing this work off-platform
without a number is a problem.

Assigning 152 as the issue number where the `F` precompile was
originally raised (ethereum#152)

* Add a missing colon

Thanks @axic 🙌

* Spelling updates

* Add @MadeofTin to the authors list

* Prefer the original issue for discussion

* Clarify the precompile's initial implementation

* Make the precompile return value clear

* Clean up references wording

* More rationale around this BLAKE2b approach

* Fix a couple misspellings

* Updated the interface for F precompile

- F precompile accepts now `abi.encodePacked` parameters taking 
exactly 213 bytes. This is safer and does not require left-padding data
- `rounds` parameter is now the first one as the gas cost depends only
on this parameter

* Updated gas cost section proposing GFROUND=1

* Detailed benchmarks moved to appendix section

* Benchmark stats are compared against ecRecover as a baseline

* Clarification: f parameter is true if it is nonzero

This rule is compatible with Solidity for boolean.

* Avoid referring to abi.encodePacked

The specification should not be Solidity-specific. Instead of
referring to abi.encodePacked we now just say "tightly encoded".

* Fixed incorrect link

"specified in the RFC" linked to the geth PR for F precompile
instead of linking to the BLAKE2b RFC.

* Shortened the description about when parameter f is considered as true

* Minor grammar improvement

* Updated information about endianness of F precompile inputs

BLAKE2b is consistently little-endian. abi.encodePacked encodes each 
of its arguments in big-endian order. We need to be clear which parameters
should go as little-endian (h, m, t) and which parameters should go as 
big-endian (rounds, f).

* Strict validation of f parameter

* Initial test vectors for F precompile

Test cases covered:
- input length too short
- input length too long
- malformed f flag encoding
- correct input, test vector from BLAKE2b RFC, Appendix A

* Test vector for a non-final round

* Test vector for the maximum number of rounds

* Test vector for a single round

* Added test vector for empty input

* The final block indicator (8-bit word) does not have endianness

* Clarify state vector encoding does not change in the output

* Put too short input test vector next to empty input test vector

* Added test vector for zero-rounds BLAKE2b case