Release notes for 1.0.0.

Move the release notes document into the docs directory, and convert to
Markdown so that it can be rendered on the project's website.

Signed-off-by: David Brown <david.brown@linaro.org>
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+# MCUboot Release Notes
+
+- Table of Contents
+{:toc}
+
+## Version 1.0.0
+
+The 1.0.0 release of MCUBoot introduces a format change.  It is
+important to either use the `imgtool.py` also from this release, or
+pass the `-2` to recent versions of the `newt` tool in order to
+generate image headers with the new format.  There should be no
+incompatible format changes throughout the 1.x.y release series.
+
+### About this release
+
+- Header format change.  This change was made to move all of the
+  information about signatures out of the header and into the TLV
+  block appended to the image.  This allows
+  - The signature to be replaced without changing the image.
+  - Multiple signatures to be applied.  This can be used, for example,
+    to sign an image with two algorithms, to support different
+    bootloader configurations based on these image.
+  - The public key is referred to by its SHA1 hash (or a prefix of the
+    hash), instead of an index that has to be maintained with the
+    bootloader.
+  - Allow new types of signatures in the future.
+- Support for PKCS#1 v1.5 signatures has been dropped.  All RSA
+  signatures should be made with PSS.  The tools have been changed to
+  reflect this.
+- The source for Tinycrypt has been placed in the MCUboot tree.  A
+  recent version of Tinycrypt introduced breaking API changes.  To
+  allow MCUboot to work across various platforms, we stop using the
+  Tinycrypt bundled with the OS platform, and use our own version.  A
+  future release of MCUboot will update the Tinycrypt version.
+- Support for some new targets:
+  - Nordic nRF51 and nRF52832 dev kits
+  - Hexiwear K64
+- Clearer sample applications have been added under `samples`.
+- Test plans for [zephyr](%{ link testplan-zephyr.md %}), and
+  [mynewt]({% link testplan-mynewt.md %}).
+- The simulator is now able to test RSA signatures.
+- There is an unimplemented `load_addr` header for future support for
+  RAM loading in the bootloader.
+- Numerous documentation.
+
+### Known issues
+
+None
+
+## Version 0.9.0
+
+This is the first release of MCUBoot, a secure bootloader for 32-bit MCUs.
+It is designed to be operating system-agnostic and works over any transport -
+wired or wireless. It is also hardware independent, and relies  on hardware
+porting layers from the operating system it works with. For the first release,
+we have support for three open source operating systems: Apache Mynewt, Zephyr
+and RIOT.
+
+### About this release
+
+- This release supports building with and running Apache Mynewt and Zephyr
+  targets.
+- RIOT is supported as a running target.
+- Image integrity is provided with SHA256.
+- Image originator authenticity is provided supporting the following
+  signature algorithms:
+  - RSA 2048 and RSA PKCS#1 v1.5 or v2.1
+  - Elliptic curve DSA with secp224r1 and secp256r1
+- Two firmware upgrade algorithms are provided:
+  - An overwrite only which upgrades slot 0 with the image in slot 1.
+  - A swapping upgrade which enables image test, allowing for rollback to a
+    previous known good image.
+- Supports both mbed-TLS and tinycrypt as backend crypto libraries. One of them
+  must be defined and the chosen signing algorithm will require a particular
+  library according to this list:
+  - RSA 2048 needs mbed TLS
+  - ECDSA secp224r1 needs mbed TLS
+  - ECDSA secp256r1 needs tinycrypt as well as the ASN.1 code from mbed TLS
+    (so still needs that present).
+
+### Known issues
+
+- The image header and TLV formats are planned to change with release 1.0:
+  https://runtimeco.atlassian.net/browse/MCUB-66