Work in progress on sink implementations. Updated parser, interpreter and engine for sink support. Engine implementations of sink endpoints and write methods remain.
Work in progress on network sinks in the engine. Revised engine and socket iohandle type. Added support for aggregated outgoing connections across virtualized peers as connection pools. Minor bugfix for role selector initializer.
Minor changes to pretty-printer instances, handles shifts better.

Known oddity: Sometimes TTuple's (and probably ETuple's) appear without
any children and look rather odd -- That's because they're a unit, and
should probably be desugared away.
Add information plumbing to fix broken tree spine issues.

The printer should be slightly more resilient to potentially missing
final entries at each tree node.
Mode-based network handle construction, and write operation implementations
Revised connection state, engine configuration, and transport. Internal connections are now treated as endpoints as well. Implemented network sends with the new approach to transports and connection state.
Rewrite pretty-printer to do tree-at-a-time printing.

This version can also do the Tuple/Unit distinction, which I've put in.
We may want a different keyword to avoid giving the impression that
Units are actual atoms in the language.
First draft of engine implementation for single-threaded execution. Latest changes include revised engine synchronization (e.g., for termination, listener thread tracking), removal of transports, listener implementations for network sources, generalized short-circuiting for messages, and simplified engine constructors.
Package dependency changes
Added finalize method to run atExit trigger, on both engine termination and error states
Merge branch 'runtime-refactor'
Merging in focus/runtime-refactor branch
Removed duplicate default addresses in interpreter and engine. Added runtime unit tests, bootstrapped with buffer tests. Added 'test' flag to cabal to support conditional module exports for exposing internal functionality.
More engine testing, including placeholders and simple datasets
Merged dtrigger branch
Merge master