Refs #2051

https://github.com/tendermint/tendermint/pull/2301

* 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

* explicitly panic if max capacity is reached

* address review comments

* comments and a test

* Implement BFT time

* set LastValidators when creating state in state helper

for heights >= 2

MaxBytes

libs/autofile: bring back loops (#2261)

* libs/autofile: bring back loops

* changelog, version

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

Refs #2035

https://github.com/tendermint/tendermint/pull/2264#issuecomment-417378396

* config: reduce default mempool size

This reduces the mempool size from 100k to 5k. Note that each secp256k1 sig
takes .5ms to compute. Therefore an adversary could previously delay every
node on the network's computation time upon receiving a block by 50 seconds.

This now reduces that ability to being able to only delay each node by 2.5
seconds. This change should be reverted once ABCI recheck is implemented.

* (squash this) fix test

Closes: #2292

* mempool: Store txs by hash inside of cache

This allows for large cachesizes, without fear of the memory
consumption growing rapidly.

* (squash this) rename hashedTx -> txHash

* update secret connection to use a little endian encoded nonce

* update encoding of chunk length to be little endian, too

* update comment

* Change comment slightly to trigger circelci

* crypto/secp256k1: Fix signature malleability, adopt more efficient encoding

This removes signature malleability per ADR 14, and makes secp match
the encoding in ADR 15.

* (squash this) add lock

* crypto/multisig: Pubkey -> PubKey

* crypto/encoding/amino: use pkg vars for routes

* crypto/multisig/bitarray

* crypto/multisig: ThresholdMultiSignaturePubKey -> PubKeyMultisigThreshold

* crypto/encoding/amino: add PubKeyMultisig to table

* remove bA import alias

https://github.com/tendermint/tendermint/pull/2255#discussion_r211900709

* db_path is not being parsed

Fix default configuration, db_path is now db_dir.

Closes: cosmos/cosmos-sdk#1712

* Update CHANGELOG_PENDING.md

* lint docs with write-good, stop-words

* remove package-lock.json

* update changelog

* fix wrong paragraph formatting

* fix some docs formatting

* fix docs format

* fix abci spec format

See https://discuss.circleci.com/t/saving-cache-stopped-working-warning-skipping-this-step-disabled-in-configuration/24423/2

Bucky/abci validators

Refs https://github.com/grpc/grpc-go/issues/2264

Add a changelog entry & Upgrading guides