cuprated: auto config docs

[Boog900]

What

closes #409

Adds a macro that generates toml comments from the doc comments.

Why

So we don't need to duplicate doc text.

Example output:

#     ____                      _
#    / ___|   _ _ __  _ __ __ _| |_ ___
#   | |  | | | | '_ \| '__/ _` | __/ _ \
#   | |__| |_| | |_) | | | (_| | ||  __/
#    \____\__,_| .__/|_|  \__,_|\__\___|
#              |_|
#
# All these config values can be set to their default by commenting them out with #.
# Some values are already commented out, to set the value remove the # at the start of the line.

## The network we should run on.
##
## Valid values: "Mainnet", "Testnet" and "Stagenet".
network = "Mainnet"
## Enable/disable fast sync.
##
## Fast sync skips verification of old blocks by comparing block hashes to a built-in hash file,
## disabling this will significantly increase sync time. New blocks are still fully validated.
fast_sync = true

## The stdout logging config.
[tracing.stdout]
## The default minimum log level.
level = "info"

## The file logging config.
[tracing.file]
## The default minimum log level.
level = "debug"
## The maximum amount of log files to keep, once this number is passed the oldest file
## will be deleted.
max_log_files = 7

## The [`tokio`] config.
##
## Tokio is the async threadpool, used for network operations and the major service inside `cuprated`.
[tokio]
## The amount of threads to spawn for the async thread-pool
#threads = 12

## The [`rayon`] config.
##
## Rayon is the CPU threadpool, used for CPU intensive tasks.
[rayon]
## The number of threads to use for the [`rayon::ThreadPool`].
#threads = 12

## The clear-net P2P config.
[p2p.clear_net]
## The IP address we should bind to to listen to connections on.
listen_on = "0.0.0.0"
## The number of outbound connections to make and try keep.
##
## Recommended to keep this value above 12.
#outbound_connections = 64
## The amount of extra connections we can make if we are under load from the rest of Cuprate.
#extra_outbound_connections = 8
## The maximum amount of inbound connections we should allow.
#max_inbound_connections = 128
## The percent of connections that should be to peers we haven't connected to before.
#gray_peers_percent = 0.7
## port to use to accept p2p connections.
##
## Set to 0 if you do not want to accept P2P connections.
p2p_port = 18080

## The address book config.
[p2p.clear_net.address_book_config]
## The size of the white peer list.
##
## The white list holds peers we have connected to before.
max_white_list_length = 1000
## The size of the gray peer list.
##
## The gray peer list holds peers we have been told about but not connected to ourself.
max_gray_list_length = 5000
## The time period between address book saves.
peer_save_period = { secs = 90, nanos = 0 }

## Block downloader config.
##
## The block downloader handles downloading old blocks from peers when we are behind.
[p2p.block_downloader]
## The size in bytes of the buffer between the block downloader and the place which
## is consuming the downloaded blocks (`cuprated`).
##
## This value is an absolute maximum, once this is reached the block downloader will pause.
#buffer_bytes = 1000000000
## The size of the in progress queue (in bytes) at which we stop requesting more blocks.
##
## The value is _NOT_ an absolute maximum, the in progress queue could get much larger. This value
## is only the value we stop requesting more blocks, if we still have requests in progress we will
## still accept the response and add the blocks to the queue.
#in_progress_queue_bytes = 500000000
## The target size of a single batch of blocks (in bytes).
##
## This value must be below 100_000_000, it is not recommended to set it above 30_000_000.
#target_batch_bytes = 10000000
## The [`Duration`] between checking the client pool for free peers.
check_client_pool_interval = { secs = 30, nanos = 0 }

## The storage config.
[storage]
## The amount of reader threads to spawn for the tx-pool and blockchain.
##
## The tx-pool and blockchain both share a single threadpool.
#reader_threads = 4

## The tx-pool config.
[storage.txpool]
## The [`SyncMode`] of the database.
##
## Changing this value could make the DB a lot slower when writing data, although
## using "Safe" makes the DB more durable if there was an unexpected crash.
##
## Valid values: ["Fast", "Safe"].
#sync_mode = "Fast"
## The maximum size of the tx-pool.
max_txpool_byte_size = 100000000

## The blockchain config.
[storage.blockchain]
## The [`SyncMode`] of the database.
##
## Changing this value could make the DB a lot slower when writing data, although
## using "Safe" makes the DB more durable if there was an unexpected crash.
##
## Valid values: ["Fast", "Safe"].
#sync_mode = "Fast"

## The filesystem config.
[fs]
## The data directory.
#data_directory = "/home/user/.local/share/cuprate"
## The cache directory.
#cache_directory = "/home/user/.cache/cuprate"

[Boog900]

@hinto-janai this is pretty much ready, just one question, what do you think we should do with the config folder. This PR would remove the need for per release files, as it is generated at runtime instead of having a static example config.

Part of me thinks we should keep them for testing backwards compatibility, just wanted to ask if you had a preference before I do anymore.

[hinto-janai]

what do you think we should do with the config folder. This PR would remove the need for per release files

Having a linkable/copyable default config is still desired for reasons I mentioned before, and yeah for backwards testing compat too.

[hinto-janai]

Automation is great, thanks for this.