Implements eth_getBlockTransactionCountByNumber

[austinabell]

• Completes Implement eth_getBlockTransactionCountByNumber #31

This does not depend on the format of tx data or receipts so can be merged in now.

To test:

1. Run the Ethermint node how it is normally run, I ran:

make install 
rm -rf ~/.emint*
emintd init moniker --chain-id testchain
emintcli config chain-id testchain
emintcli config output json
emintcli config indent true
emintcli config trust-node true
emintcli keys add austin
<password>
<password>
emintd add-genesis-account $(emintcli keys show austin -a) 1000photon,100000000stake
emintd gentx --name austin
<password>
emintd collect-gentxs
emintd validate-genesis
emintd start

2. Start rest server:

emintcli rest-server --laddr "tcp://localhost:8545"

3. Send request:

curl -X POST --data '{"jsonrpc":"2.0","method":"eth_getBlockTransactionCountByNumber","params":["0x1"],"id":1}' -H "Content-Type: application/json" http://localhost:8545/rpc
 > {"jsonrpc":"2.0","id":1,"result":"0x0"}

Since txs can't be sent currently, it will always be 0, but I have tested with manual values that it correctly outputs other values if that is what is pulled from the TM node.

[ansermino]

I want to say this will fail if a block number greater than the current block number is passed (can't confirm rn) and then we will get a panic on the next line

[austinabell]

yeah I'll add error handling for this. I was trying to follow the eth code but it doesn't make sense why error handling doesn't exist for this