Fix syncing bugs by recursively attempting to process parents in the … (#429)

* Fix syncing bugs by recursively attempting to process parents in the import queue, change BlockRootsIterator

* Swap from crossbeam channel to tokio mpsc

* Recursion fix

* Remove exess block processing

* Fix network lag, correct attestation topic

* Correct network poll logic

* Overhaul of SimpleSync and modify BlockRootsIterator to return start_slot

* Fix bug in tests relating to StateRootsIterator

* Remove old, commented-out heartbeat code.

* Tidy docs on import queue enum

* Change source logging msg in simple sync

* Rename function parameter in simple sync

* Use `BestBlockRootsIterator` in `reduced_tree`

* Update comments for `BestBlockRootsIterator`

* Fix duplicate dep in cargo.toml

beacon_node/http_server/Cargo.toml

@@ -27,9 +27,8 @@ futures = "0.1.23"
 serde = "1.0"
 serde_derive = "1.0"
 serde_json = "1.0"
-slog = "^2.2.3"
+slog = { version = "^2.2.3" , features = ["max_level_trace"] }
 slog-term = "^2.4.0"
 slog-async = "^2.3.0"
 tokio = "0.1.17"
 exit-future = "0.1.4"
-crossbeam-channel = "0.3.8"