Add note in Changelog about caching
## v0.15.0-dev
+ * Completely rewritten caching layer. This has the following improvements;
+ * OS caching no longer used on Linux. Direct I/O is used now with the
+ caching internal to fwup. For large archives, this results in about
+ a 10% performance improvement. More importantly, fwup can provide more
+ confidence that the final write to swap A/B partitions actually happens
+ last.
+ * Flash erase block aligned writes - currently hardcoded to 128 KB. This may
+ be helpful for some devices even though it doesn't appear to improve
+ performance.
+ * One cache - previously there were limited ones for FAT operations and raw
+ writes. This removed some code and the new implementation is simpler.
+ * Support for discarding unused blocks and hardware TRIM
+ * Unit tests now validate read and write syscalls for alignment, size and
+ final order on Linux using ptrace.
+ * The progress indicator now moves more linearly rather than racing to 99%
+ and hanging for a while.
+
+ * New features
+ * trim() command to discard storage regions. This avoids read/modify/write
+ operations from being issued by fwup on smaller than erase-block sized
+ writes.
+ * `--enable-trim` option to enable the sending of hardware TRIM commands to
+ devices that support them.
+
* Bug fixes
* Fix segfault if a bad value is specified in the u-boot environment block.
* Silence eject failure warning on OSX that appears to be harmless. Fixes
