Port PubSub to Registry

With this, we start the work on Phoenix.PubSub v2.0.

Author: José Valim

.gitignore

@@ -1,5 +1,6 @@
 /_build
 /cover
 /deps
+/doc
 erl_crash.dump
 *.ez

.travis.yml

@@ -1,18 +1,12 @@
 language: elixir
-elixir:
-  - 1.4
-  - 1.5
-  - 1.6
-otp_release:
-  - 19.3
-  - 20.3
-  - 21.0
+elixir: 1.6
+otp_release: 19.3
 matrix:
-  exclude:
-    - elixir: 1.5
-      otp_release: 21.0
-    - elixir: 1.4
-      otp_release: 21.0
+  include:
+    - elixir: 1.7
+      otp_release: 20.3
+    - elixir: 1.8
+      otp_release: 21.3
 sudo: false
 before_script:
   - epmd -daemon

CHANGELOG.md

@@ -1,42 +1,6 @@
 # Changelog
 
-## v1.1.2 (2019-02-23)
+This new version of Phoenix.PubSub provides a simpler, more extensible, and more performant Phoenix.PubSub API. For users of Phoenix.PubSub, the API is the same, although frameworks and other adapters will have to migrate accordingly (which often means less code).
 
-* Bug fixes
-  * Avoid warnings when running on Elixir v1.8
+## v2.0.0-dev
 
-## v1.1.1 (2018-10-17)
-
-* Bug fixes
-  * Fix issue causing empty deltas to be chosen for replication
-  * Improve replication over netsplit
-
-## v1.1.0 (2018-08-10)
-
-* Enhancements
-  * Optimize Tracker CRDT operations for increased performance
-  * Shard tracker internally to use pool of trackers for increased performance under load
-  * [Tracker] Add `get_by_key/3` to lookup a single presence entry for a given topic and key
-
-## v1.0.2 (2017-06-14)
-
-* Enhancements
-  * Support `child_spec` in `PG2` adapter
-
-* Bug fixes
-  * Fix presence "zombies" / "ghosts" caused by replicas receiving downed pids for remote replicas they never observe
-
-## v1.0.1 (2016-09-29)
-
-* Enhancements
-  * Support passing a function to `Tracker.update` for partial metadata updates
-  * Prevent duplicate track registrations when calling `Tracker.track`
-
-* Bug fixes
-  * [PG2] - Fix multinode broadcasts requiring the same pool_size to properly broker messages
-
-## v1.0.0 (2016-06-23)
-
-* Enhancements
-  * Extract `Phoenix.PubSub` into self-contained application
-  * Add `Phoenix.Tracker` for distributed presence tracking for processes