Wtfix

**Fixes**

- Prevent a pipeline shutdown from being triggered multiple times.
- Less verbose logging of connection errors that occur during shutdown / logout.

**Enhancements**

- Repeating group templates can now be configured on a per-message-type basis.

**Enhancements**

- Make username and password optional for Logon messages.
- Fixed an issue that caused only one Heartbeat timer to be used for both sending and receiving messages.
- Collections of FIXMessages can now be sorted by their sequence numbers.

**Fixes**

- Set `SendingTime` before message is added to the message store (Fixes [2](https://github.com/jcass77/WTFIX/issues/2)).
- Enforce serial processing: wait until a message has been propagated through the entire pipeline before receiving the next message.

**Enhancements**

- Automatically start a new session if no relevant .sid file can be found.
- Heartbeat monitor now proactively sends heartbeats as well, in compliance with the FIX protocol specification.
- Pipeline now shuts down gracefully on SIGTERM and SIGINT signals in addition to CTRL+C.

**Fixes**

- Fix path to .sid files.

**Enhancements**

- Added RedisPubSubApp for sending / receiving messages using the redis Pub/Sub messaging paradigm.
- Various performance optimizations.

**Fixes**

- Add missing dependencies to setup.py.

**Enhancements**

- FIX sessions are now resumed between different connections by default. Pass parameter `-new_session` when calling
the pipeline in order to reset sequence numbers and initialize a new session.
- Rename 'sessions' to 'connections' to align with FIX protocol terminology.
- Gap fill processing is now more reliable, and will queue messages that are received out of order until the gaps have
been filled.
- Set exit codes on pipeline termination so that caller can take appropriate action.
- Add `MessageStoreApp`, with default implementations for in-memory and redis-based stores for caching and / or
persisting messages to database.
- Convert all `on_send` and `on_receive` handlers to async and await.
- Messages are now sent in separate Tasks to avoid holding up the main event loop.
- AuthenticationApp now blocks all incoming and outgoing messages until authentication has been completed.