Vulnerabilities

Fixes a vulnerability where a properly crafted SSH client can bypass user
authentication in the wolfSSH server code. The added fix filters the
messages that are allowed during different operational states.

Notes

When building wolfSSL/wolfCrypt versions before v5.6.6 with CMake,
wolfSSH may have a problem with RSA keys. This is due to wolfSSH not
checking on the size of ___uint128_t. wolfSSH sees the RSA structure
as the wrong size. You will have to define HAVE___UINT128_T if you
know you have it and are using it in wolfSSL. wolfSSL v5.6.6 exports that
define in options.h when using CMake.
The example server in directory examples/server/server.c has been removed.
It was never kept up to date, the echoserver did its job as an example and
test server.

Added functions to set algorithms lists for KEX at run-time, and some
functions to inspect which algorithms are set or are available to use.
In v1.4.15, we had disabled SHA-1 in the build by default. SHA-1 has been
re-enabled in the build and is now "soft" disabled, where algorithms using
it can be configured for KEX.
Add Curve25519 KEX support for server/client key agreement.

Clean up some issues when building for Nucleus.
Clean up some issues when building for Windows.
Clean up some issues when building for QNX.
Added more wolfSSHd testing.
Added more appropriate build option guard checking.
General improvements for the ESP32 builds.
Better terminal support in Windows.
Better I/O pipes and return codes when running commands or scripts over an
SSH connection.