Preps for 1.8.0-rc1

[travis]: https://travis-ci.org/mcu-tools/mcuboot

[license]: https://github.com/mcu-tools/mcuboot/blob/main/LICENSE

This is mcuboot version 1.8.0-dev

This is mcuboot version 1.8.0-rc1

MCUboot is a secure bootloader for 32-bit MCUs. The goal of MCUboot is to

define a common infrastructure for the bootloader, system flash layout on

- Table of Contents

{:toc}

## Version 1.8.0

The 1.8.0 release of MCUboot contains numerous fixes, and adds support

for the NuttX RTOS, and the Espressif ESP32 SDK.

### About this release

- Add support for the NuttX RTOS.

- Add support for the Espressif ESP32 SDK.

- `boot_serial` changed to use cddl-gen, which removes the dependency

  on tinycbor.

- Add various hooks to be able to change how image data is accessed.

- Cypress supports Mbed TLS for encryption.

- Support using Mbed TLS for ECDSA.  This can be useful if Mbed TLS is

  brought in for another reason.

- Add simulator support for testing direct-XIP and ramload.

- Support Mbed TLS 3.0.  Updates the submodule for Mbed TLS to 3.0.

- Enable direct-xip mode in mbed-os port.

- extract `bootutil_public` library, a common interface for mcuboot

  and the application.

- Allow to boot primary image if secondary one is unreachable.

- Add AES256 image encryption support.

- Add Multiimage boot for direct-xip and ram-load mode.

### Security fixes

- [GHSA-gcxh-546h-phg4](https://github.com/mcu-tools/mcuboot/security/advisories/GHSA-gcxh-546h-phg4)

  has been published.  There is not a fix at this time, but a caution

  to be sure to follow the instructions carefully, and make sure that

  the development keys in the repo are never used in a production

  system.

## Version 1.7.0

The 1.7.0 release of MCUBoot adds support for the Mbed-OS platform,

    "1.7.0": "v1.7.0"

    "1.7.1": "v1.7.1"

    "1.7.2": "v1.7.2"

    "1.8.0": "v1.8.0-rc1"

    "0-dev": "0.0.0"        # main

    "0-latest": "1.7.2"     # latest stable release

# See the License for the specific language governing permissions and

# limitations under the License.

imgtool_version = "1.7.0"

imgtool_version = "1.8.0rc1"