docs: add a Speedb HISTORY file (#100)

Add a change log file in the same format as the RocksDB one to track changes
between released versions. Currently this contains an abbreviated change
log for version 2.0.0, but not any of the changes that landed since then.

HISTORY.md

@@ -0,0 +1,40 @@
+# Speedb Change Log
+
+## Unreleased
+
+Based on RocksDB 7.2.2
+
+### New Features
+
+### Bug Fixes
+
+### Behavior Changes
+
+### Performance Improvements
+
+### Public API changes
+
+### Java API Changes
+
+## 2.0.0
+
+Based on RocksDB 7.2.2
+
+### New Features
+
+ * Added a new experimental hash-based memtable with more granular locking (#30)
+ * Added ability to create `MemTableFactory` from URI/string to tools (#72)
+
+### Bug Fixes
+
+ * Avoid comparing Status using == as it compares only status codes but not subcodes
+ * examples: fix snapshots leak in `optimistic_transaction_example`
+ * ldb: fix the `get` command to print the entire value
+ * db_bench: fix a bug in handling multiple DBs that caused a `last_ref` assertion
+ * db_bench: fix `SeekRandom` and `ReadRandomWriteRandom` to work on all CFs instead of only the default
+ * db_bench: report accurate read response time when using a rate limit
+
+### Miscellaneous
+
+ * Add test for forwarding the incomplete status on `no_io` (an addition to facebook/rocksdb#8485)
+ * CMake: fix the plugin infra and add support for `*_FUNC` registration