Update changelog for v1.0.

Change-Id: I0edc584b0b4166518f3afef777dada4a9c47f3b9

CHANGELOG.md

@@ -1,3 +1,22 @@
+## 1.0.0 (2020-05-27)
+
+First full release! Public API is stable from this point onward.
+
+New Features (not exhaustive):
+- Generic media pipeline allowing apps to replace media components
+- Offline storage and playback support
+- Use native AVPlayer for HLS
+ - Controllable with `streaming.useNativeHlsOnSafari` configuration
+ - Exposes the AVPlayer instance for app control
+- Don't use FFmpeg decoders to reduce binary size
+- Removes SDL to reduce binary size
+- Better Swift support
+- Network request/response filters
+- Playback of HEVC content
+- Honors sample aspect ratio (SAR)
+- Allow setting video fill mode
+
+
 ## 0.1.0-beta (2018-11-30)
 
 Initial beta launch!