tinysshnoneauthd

add -e param., allow to execute custom program instead of shell

but don't close the connection

fixes #39

README.md update

honor "max packet size" requested from the client

sntrup761x25519 sha512@openssh.com

fix: MSG_USERAUTH_SUCCESS should be alone without extra bits

fix path logged when authorized_keys cannot be open/read

The path passed to `subprocess_auth_authorizedkeys_` is the user's home
directory, but we're trying to read `~/.ssh/authorized_keys` - the
logged path should include a `.ssh`.

Use correct 'ar' invocation when cross-compiling.

Make cross compile accessible in Makefile