conesnsu: follow up to removing some consensus params (#2427)

* 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
https://github.com/tendermint/go-amino/blob/0c74291f3bb61e24f8ea1d13148cece479f79d35/encoder.go#L85-L90
* avoid cyclic imports
* you can do better Go, come on
* remove testdouble package

docs/spec/README.md

@@ -21,6 +21,7 @@ please submit them to our [bug bounty](https://tendermint.com/security)!
 ### Consensus Protocol
 
 - [Consensus Algorithm](/docs/spec/consensus/consensus.md)
+- [Creating a proposal](/docs/spec/consensus/creating-proposal.md)
 - [Time](/docs/spec/consensus/bft-time.md)
 - [Light-Client](/docs/spec/consensus/light-client.md)
 

docs/spec/consensus/creating-proposal.md

@@ -0,0 +1,42 @@
+# Creating a proposal
+
+A block consists of a header, transactions, votes (the commit),
+and a list of evidence of malfeasance (ie. signing conflicting votes).
+
+We include no more than 1/10th of the maximum block size
+(`ConsensusParams.BlockSize.MaxBytes`) of evidence with each block.
+
+## Reaping transactions from the mempool
+
+When we reap transactions from the mempool, we calculate maximum data
+size by subtracting maximum header size (`MaxHeaderBytes`), the maximum
+amino overhead for a block (`MaxAminoOverheadForBlock`), the size of
+the last commit (if present) and evidence (if present). While reaping
+we account for amino overhead for each transaction.
+
+```go
+func MaxDataBytes(maxBytes int64, valsCount, evidenceCount int) int64 {
+	return maxBytes -
+		MaxAminoOverheadForBlock -
+		MaxHeaderBytes -
+		int64(valsCount)*MaxVoteBytes -
+		int64(evidenceCount)*MaxEvidenceBytes
+}
+```
+
+## Validating transactions in the mempool
+
+Before we accept a transaction in the mempool, we check if it's size is no more
+than {MaxDataSize}. {MaxDataSize} is calculated using the same formula as
+above, except because the evidence size is unknown at the moment, we subtract
+maximum evidence size (1/10th of the maximum block size).
+
+```go
+func MaxDataBytesUnknownEvidence(maxBytes int64, valsCount int) int64 {
+	return maxBytes -
+		MaxAminoOverheadForBlock -
+		MaxHeaderBytes -
+		int64(valsCount)*MaxVoteBytes -
+		MaxEvidenceBytesPerBlock(maxBytes)
+}
+```