Add REST and RPC clients to lightning-block-sync

Implements a simple HTTP client that can issue GET and POST requests.
Used to implement REST and RPC clients, respectively. Both clients
support either blocking or non-blocking I/O.

Author: jkczyz

lightning-block-sync/Cargo.toml

@@ -8,6 +8,17 @@ description = """
 Utilities to fetch the chain data from a block source and feed them into Rust Lightning.
 """
 
+[features]
+rest-client = [ "serde_json", "chunked_transfer" ]
+rpc-client = [ "serde_json", "chunked_transfer" ]
+
 [dependencies]
 bitcoin = "0.24"
 lightning = { version = "0.0.12", path = "../lightning" }
+tokio = { version = "1.0", features = [ "io-util", "net" ], optional = true }
+serde_json = { version = "1.0", optional = true }
+chunked_transfer = { version = "1.4", optional = true }
+futures = { version = "0.3" }
+
+[dev-dependencies]
+tokio = { version = "1.0", features = [ "macros", "rt" ] }