Plugins: add ssh-base ssh server plugin

CMakeLists.txt

READMEs/README-plugin-sshd-base.md

READMEs/README.lwsws.md

cmake/lws_config.h.in

lib/context.c

lib/lejp-conf.c

lib/libwebsockets.c

lib/libwebsockets.h

lib/server.c

lib/ssl-client.c

plugins/protocol_lws_sshd_demo.c

plugins/ssh-base/crypto/chacha.c

plugins/ssh-base/crypto/ed25519.c

plugins/ssh-base/crypto/fe25519.c

plugins/ssh-base/crypto/fe25519.h

plugins/ssh-base/crypto/ge25519.c

plugins/ssh-base/crypto/ge25519.h

plugins/ssh-base/crypto/ge25519_base.data

plugins/ssh-base/crypto/poly1305.c

plugins/ssh-base/crypto/sc25519.c