Allow sending messages to registered process with `!`

[UncleGrumpy]

Enables sending messages to registered processes using the shorthand ! operator. If a message is sent to an atom name that is not registered using the ! operator a badarg run-time error occurs, matching OTP behaviour.

Closes #1011 Closes #98

These changes are made under both the "Apache 2.0" and the "GNU Lesser General Public License 2.1 or later" license terms (dual license).

SPDX-License-Identifier: Apache-2.0 OR LGPL-2.1-or-later