daemon-rpc: incorrect doc fixes

[hinto-janai]

What

Fixes incorrect documentation for daemon RPC calls; requires review into monerod.

Fixes

Table of fixes in this PR, originally tracked here: https://github.com/Cuprate/cuprate/issues/159.

Route/endpoint	Link	Notes
get_miner_data	get_miner_data, rpc/core_rpc_server_commands_defs.h @ 1012	difficulty field is noted as unsigned int, although it is actually a JSON string containing an unsigned int in hex form. Other documentation describes these hex int strings as string.
calc_pow	calc_pow, cryptonote_basic/blobdatatype.h @ 39	Type used to describe block_data is blobdata. This is a monerod-specific type alias to std::string. Documentation should explain that it is a hex-encoded string of a block.
/get_outs.bin	get_outs.bin, rpc/core_rpc_server_commands_defs.h @ 538..544	Documentation mentions non-existent field: amount
/send_raw_transaction	send_raw_transaction, rpc/core_rpc_server_commands_defs.h @ 629..663	Documentation mentions non-existent field: not_rct
/mining_status	mining_status, core_rpc_server_commands_defs.h @ 857..873	Documentation notates numbers as int instead of unsigned int. These are unsigned int both in code and elsewhere in documentation.
/get_transaction_pool	get_transaction_pool, rpc/core_rpc_server_commands_defs.h @ 1524	Missing documentation for weight field, should be unsigned int; <DESCRIPTION>
flush_txpool	flush_txpool	Empty "" transaction in example causes error
get_block	get_block	Documentation states for tx_hashes field: "If there are no other transactions, this will be an empty list." This is not true, monerod's serializer will omit fields completely if the container is empty. The tx_hashes in the json field will exist, however.

Simple proof for get_block:

curl \
    http://127.0.0.1:18081/json_rpc \
    -d '{"jsonrpc":"2.0","id":"0","method":"get_block","params":{"height":0}}' \
    -H 'Content-Type: application/json'