* WIP: switching to fixed offsets for SignBytes

* add version field to sign bytes and update order

* more comments on test-cases and add a tc with a chainID

* remove amino:"write_empty" tag

- it doesn't affect if default fixed size fields ((u)int64) are
written or not
- add comment about int->int64 casting

* update CHANGELOG_PENDING

* update documentation

* add back link to issue #1622 in documentation

* remove JSON tags and add (failing test-case)

* fix failing test

* update test-vectors due to added `Type` field

* change Type field from string to byte and add new type alias

- SignedMsgType replaces VoteTypePrevote, VoteTypePrecommit and adds new
ProposalType to separate votes from proposal when signed

- update test-vectors

* fix remains from rebasing

* use SignMessageType instead of byte everywhere

* fixes from review

* switch to amino for SignBytes and add Reply with error message

- currently only Vote is done

* switch Reply type in socket for other messages

 - add error description on error

* add TODOs regarding error handling

* address comments from peer review session (thx @xla)

 - contains all changes besides the test-coverage / error'ing branches

* increase test coverage:

 - add tests for each newly introduced error'ing code path

* return error if received wrong response

* add test for wrong response branches (ErrUnexpectedResponse)

* update CHANGELOG_PENDING and related documentation (spec)

* fix typo: s/CanonicallockID/CanonicalBlockID

* fixes from review

* follow up to removing some consensus params Refs #2382
* change args type to int64 in state#makeParams
* make valsCount and evidenceCount ints again
* MaxEvidenceBytesPerBlock: include magic number in godoc
* [spec] creating a proposal
* test state#TxFilter
* panic if MaxDataBytes is less than 0
* fixes after review
* use amino#UvarintSize to calculate overhead
0c74291f3b/encoder.go (L85-L90)
* avoid cyclic imports
* you can do better Go, come on
* remove testdouble package

* ReapMaxTxs: return all txs if max is negative

this mirrors ReapMaxBytes behavior

See https://github.com/tendermint/tendermint/pull/2184#discussion_r214439950

* increase MaxAminoOverheadForBlock

tested with:

```
func TestMaxAminoOverheadForBlock(t *testing.T) {

        maxChainID := ""
        for i := 0; i < MaxChainIDLen; i++ {
                maxChainID += "𠜎"
        }

        h := Header{
                ChainID:            maxChainID,
                Height:             10,
                Time:               time.Now().UTC(),
                NumTxs:             100,
                TotalTxs:           200,
                LastBlockID:        makeBlockID(make([]byte, 20), 300, make([]byte, 20)),
                LastCommitHash:     tmhash.Sum([]byte("last_commit_hash")),
                DataHash:           tmhash.Sum([]byte("data_hash")),
                ValidatorsHash:     tmhash.Sum([]byte("validators_hash")),
                NextValidatorsHash: tmhash.Sum([]byte("next_validators_hash")),
                ConsensusHash:      tmhash.Sum([]byte("consensus_hash")),
                AppHash:            tmhash.Sum([]byte("app_hash")),
                LastResultsHash:    tmhash.Sum([]byte("last_results_hash")),
                EvidenceHash:       tmhash.Sum([]byte("evidence_hash")),
                ProposerAddress:    tmhash.Sum([]byte("proposer_address")),
        }
        b := Block{
                Header:     h,
                Data:       Data{Txs: makeTxs(10000, 100)},
                Evidence:   EvidenceData{},
                LastCommit: &Commit{},
        }

        bz, err := cdc.MarshalBinary(b)
        require.NoError(t, err)

        assert.Equal(t, MaxHeaderBytes+MaxAminoOverheadForBlock-2, len(bz)-1000000-20000-1)
}
```

* fix MaxYYY constants calculation

by using math.MaxInt64

See https://github.com/tendermint/tendermint/pull/2184#discussion_r214444244

* pass mempool filter as an option

See https://github.com/tendermint/tendermint/pull/2184#discussion_r214445869

* fixes after Dev's comments

See ADR 020: Limiting txs size inside a block docs/architecture/adr-020-block-size.md

Refs #2035

Currently the top level directory contains basically all of the code
for the crypto package. This PR moves the crypto code into submodules
in a similar manner to what `golang/x/crypto` does. This improves code
organization.

Ref discussion: https://github.com/tendermint/tendermint/pull/1966

Closes #1956

This reverts commit 58d0c8de89.

remove test for String (very brittle)

This reverts commit d02c5d1e30.

This reverts commit 96a3502

exampleVote doesn't express the type of the vote.

String() and Proposal valid after serializing.
To be safe, but mainly to increase test coverage for the PR

types/vote_test.go now checks signature on a serialized and
then deserialized vote. Turns out go-wire time encoding doesn't
respect timezones, and the signatures don't check out.