Problem: CHANGELOG.md isn't updated for the 2.0 Alpha release (#2159)

* Update CHANGELOG.md for the 2.0 release

* Problem: BigchainDB 2.0 Alpha name & tag wrong in CHANGELOG.md

Solution: Name="BigchainDB 2.0 Alpha" tag="v2.0.0a1"

* Problem: Blogpost link missing & no Known Issues

Solution: Hyperlink the blog post with the missing link and
document the Known Issues.

* Problem: The 2.0 Alpha release date in CHANGELOG.md was wrong

Solution: Changed the release date of 2.0 Alpha to April 3, 2018 in CHANGELOG.md

CHANGELOG.md

@@ -2,25 +2,10 @@
 
 All _notable_ changes to this project will be documented in this file (`CHANGELOG.md`).
 
-This project adheres to [the Python form of Semantic Versioning](https://packaging.python.org/tutorials/distributing-packages/#choosing-a-versioning-scheme) (or at least we try).
-
-The BigchainDB **public API**
-* includes:
-  * This definition of **public API**.
-  * The configuration defaults, schemas, and paths where configuration files are stored.
-  * The Command Line Interface.
-  * The transaction schema.
-  * All the endpoints exposed by the HTTP API (including payloads sent to and received from them).
-  * The WebSocket Event Stream API.
-  * The docker setup.
-* excludes:
-  * **Everything** marked as `experimental` (even if the feature is part of the **public API**).
-  * The logs generated by the server.
-  * The internal API, such as classes, methods, functions.
-
-
-Contributors to this file, please follow the guidelines on [keepachangelog.com](http://keepachangelog.com/).
-Note that each version (or "release") is the name of a [Git _tag_](https://git-scm.com/book/en/v2/Git-Basics-Tagging) of a particular commit, so the associated date and time are the date and time of that commit (as reported by GitHub), _not_ the "Uploaded on" date listed on PyPI (which may differ).
+This project adheres to [the Python form of Semantic Versioning](https://packaging.python.org/tutorials/distributing-packages/#choosing-a-versioning-scheme) (or at least we try). The BigchainDB public API _was_ defined in this file but that definition was moved and can now be found in [BEP-7](https://github.com/bigchaindb/BEPs/tree/master/7).
+
+Contributors to this file, please follow the guidelines on [keepachangelog.com](http://keepachangelog.com/). Note that each version (or "release") is the name of a [Git _tag_](https://git-scm.com/book/en/v2/Git-Basics-Tagging) of a particular commit, so the associated date and time are the date and time of that commit (as reported by GitHub), _not_ the "Uploaded on" date listed on PyPI (which may differ).
+
 For reference, the possible headings are:
 
 * **Added** for new features.
@@ -32,6 +17,29 @@ For reference, the possible headings are:
 * **External Contributors** to list contributors outside of BigchainDB GmbH.
 * **Notes**
 
+## [2.0 Alpha] - 2018-04-03
+
+Tag name: v2.0.0a1
+
+There were _many_ changes between 1.3 and 2.0 Alpha, too many to list here. We wrote a series of blog posts to summarize most changes, especially those that affect end users and application developers:
+
+* [BigchainDB 2.0 is Byzantine Fault Tolerant](https://blog.bigchaindb.com/bigchaindb-2-0-is-byzantine-fault-tolerant-5ffdac96bc44)
+* [Some HTTP API Changes in the Next Release](https://blog.bigchaindb.com/some-http-api-changes-in-the-next-release-49612a537b0c)
+* [Three Transaction Model Changes in the Next Release](https://blog.bigchaindb.com/three-transaction-model-changes-in-the-next-release-dadbac50094a)
+* [Changes to the Server Command Line Interface in BigchainDB 2.0](https://blog.bigchaindb.com/changes-to-the-server-command-line-interface-in-bigchaindb-2-0-e1d6576e7155)
+* _A forthcoming post about changes in BigchainDB Server configuration settings_
+
+### External Contributors
+
+* @r7vme contributed [pull request #1984](https://github.com/bigchaindb/bigchaindb/pull/1984) which fixed a bug in our Kubernetes-based production deployment template.
+
+### Known Issues
+
+We intend to resolve these issues before releasing the final BigchainDB 2.0:
+
+* There's a known Heisenbug that (sometimes) arises and we found that making the BigchainDB webserver single-threaded prevents that bug from causing problems. We intend to resolve that bug, but in the meantime our temporary workaround is to change the _default_ webserver configuration settings to single-threaded mode, i.e. `BIGCHAINDB_SERVER_WORKERS=1` and `BIGCHAINDB_SERVER_THREADS=1`.
+* Issues sometimes happen when a large transaction is sent to a BigchainDB network.
+
 ## [1.3] - 2017-11-21
 Tag name: v1.3.0