Changelog updates (#93)

* Add a couple more missing changelog entries

* Acknowledge third-party contributions

* Add release date

Author: mdickinson

CHANGELOG.rst

@@ -1,10 +1,14 @@
 What's new in bigfloat 0.4.0?
 =============================
 
+Release date: 2019-12-30
+
 This minor release adds a number of small features, changes the default
 context to match IEEE 754 quadruple precision (binary128), and fixes support
 for recent Python versions.
 
+Thanks to Hugo van Kemenade for contributions to this release.
+
 New Features
 ------------
 
@@ -28,7 +32,7 @@ Changes
 -------
 
 - The default context now matches IEEE 754 quadruple precision instead
-  of double precision. (#72)
+  of double precision. (#72, #89, #87)
 
 - Infinities and NaNs are now represented as 'inf' and 'nan' rather
   than 'Infinity' and 'NaN', for consistency with the float type, and
@@ -52,6 +56,10 @@ Bugfixes
 - Fix a test failure with Mpfr 4.0, that was due a change in the value
   of ``MPFR_PREC_MIN``. (#77)
 
+- Fix initialization of the context on background threads. (#91)
+
+- Fix unit tests that changed the context and didn't reset their changes. (#92)
+
 Documentation
 -------------