update the CHANGELOG with some missing changes.
missed to add these with some merged PRs
## master / unreleased
- - [ENHANCEMENT] Time-ovelapping blocks are now allowed. [#370](https://github.com/prometheus/tsdb/pull/370)
+ - [FEATURE] Time-ovelapping blocks are now allowed. [#370](https://github.com/prometheus/tsdb/pull/370)
+ - Disabled by default and can be enabled via `AllowOverlappingBlock` option.
- Added `MergeChunks` function in `chunkenc/xor.go` to merge 2 time-overlapping chunks.
- Added `MergeOverlappingChunks` function in `chunks/chunks.go` to merge multiple time-overlapping Chunk Metas.
- Added `MinTime` and `MaxTime` method for `BlockReader`.
- - [CHANGE] `NewLeveledCompactor` takes a context so that a compaction is canceled when closing the db.
+ - [FEATURE] New `dump` command to tsdb tool to dump all samples.
+ - [FEATURE] New `encoding` package for common binary encoding/decoding helpers.
+ - Added to remove some code duplication.
- [ENHANCEMENT] When closing the db any running compaction will be cancelled so it doesn't block.
+ - `NewLeveledCompactor` takes a context.
- [CHANGE] `prometheus_tsdb_storage_blocks_bytes_total` is now `prometheus_tsdb_storage_blocks_bytes`
+
## 0.4.0
- [CHANGE] New `WALSegmentSize` option to override the `DefaultOptions.WALSegmentSize`. Added to allow using smaller wal files. For example using tmpfs on a RPI to minimise the SD card wear out from the constant WAL writes. As part of this change the `DefaultOptions.WALSegmentSize` constant was also exposed.
- [CHANGE] Empty blocks are not written during compaction [#374](https://github.com/prometheus/tsdb/pull/374)
