update CHANGELOG and bump version to 3.0.0

Signed-off-by: Benjamin Wohlwend <[email protected]>

Author: beniwohli

CHANGELOG.md

@@ -1,8 +1,8 @@
 # Changelog
 
-## Unreleased
+## v3.0.0
 
-[Check the diff](https://github.com/elastic/apm-agent-python/compare/v2.2.1...master)
+[Check the diff](https://github.com/elastic/apm-agent-python/compare/v2.2.1...v3.0.0)
 
  - adapted "black" code formatter for this repository (#262)
  - **BREAKING**: dropped support for Python 3.3 (#242) 

elasticapm/version.py

@@ -1,2 +1,2 @@
-__version__ = (2, 2, 1)
+__version__ = (3, 0, 0)
 VERSION = ".".join(map(str, __version__))