Add Changelog in preparation for v0.3 release

ChangeLog

+2022-01-18  Utz-Uwe Haus  <uhaus@C02ZD3QXLVDR>
+
+	* Release 0.3
+
+	* Major changes:
+	- Include libfabric 1.14.0
+	- Include mamba 0.1.9
+
+	* New features:
+
+	- DISPOSE-and-REUSE functionality
+
+	- proper support for multi-ranked applications (using component-index in addition
+	  to component name)
+
+	- (limited) support for distributed CDOs
+
+	- documentation on https://maestro-core.readthedocs.io/
+
+	- OFI endpoint serialization using a protobuf-based format, and a tool to decode
+	 pool manager info to human-readable form (tests/decode_pm_info)
+
+	- asynchronous CDO operations
+
+
+
+	* Other notable changes:
+
+	- add origin-side timestamp to pool protocol events, expose in application-side events
+
+	- numerous performance enhancements and memory leak fixes
+
+	- Default to DRC node insecure mode by switching to
+	  DRC_FLAGS_FLEX_CREDENTIAL (can be disabled). This solves the problem of using GNI from
+	  multiple applications on the same compute node.
+
+	- Streamlined logging, especially on the pool manager when not doing DEBUG level tracing
+
+	- aggressive CDO state change checking, ensuring invalid state changes are detected early.
+
+	- cleaner handling of rejected JOIN (e.g., if trying to join twice with the same IDs)
+
+	- proper support for 0-sized CDOs
+
+	- better sepation of data for GFS transport
+
+	- default to low-debugging compilation unless --enable-developer configure flag is given
+
+
+
+2021-09-20  Utz-Uwe Haus  <uhaus@hpe.com>
+
+	* Release 0.2, commit 519fea863b3fc5cf8f8fb568c1220836e37dc3be
+	First stable release of maestro core.
+