Add more comments about the hard-coded limits (#4100)

* crypto: expose MaxAunts for documentation purposes

* types: update godoc for new maxes

* docs: make hard-coded limits more explicit

* wal: add todo to clarify max size

* shorten lines in test

docs/spec/blockchain/blockchain.md

@@ -434,6 +434,8 @@ All votes must have a valid signature from the corresponding validator.
 The sum total of the voting power of the validators that voted
 must be greater than 2/3 of the total voting power of the complete validator set.
 
+The number of votes in a commit is limited to 10000 (see `types.MaxVotesCount`).
+
 ### Vote
 
 A vote is a signed message broadcast in the consensus for a particular block at a particular height and round.

docs/spec/blockchain/encoding.md

@@ -155,7 +155,9 @@ See details of SimpleProof, below.
 ### MakeParts
 
 Encode an object using Amino and slice it into parts.
-Tendermint uses a part size of 65536 bytes.
+Tendermint uses a part size of 65536 bytes, and allows a maximum of 1601 parts
+(see `types.MaxBlockPartsCount`). This corresponds to the hard-coded block size
+limit of 100MB.
 
 ```go
 func MakeParts(block Block) []Part
@@ -288,7 +290,9 @@ func computeHashFromAunts(index, total int, leafHash []byte, innerHashes [][]byt
 }
 ```
 
-The number of aunts is limited to 100 (`maxAunts`) to protect the node against DOS attacks.
+The number of aunts is limited to 100 (`MaxAunts`) to protect the node against DOS attacks.
+This limits the tree size to 2^100 leaves, which should be sufficient for any
+conceivable purpose.
 
 ### IAVL+ Tree
 

docs/spec/blockchain/state.md

@@ -27,6 +27,9 @@ type State struct {
 }
 ```
 
+Note there is a hard-coded limit of 10000 validators. This is inherited from the
+limit on the number of votes in a commit.
+
 ### Result
 
 ```go