add returnTermination config to TextSerialCom

What

This MR adds a returnTermination configuration parameter to TextSerialCom. This allows for the "asymmetric" send/receive termination characters mentioned in #101 (closed).

By default, the return termination characters are set to be the same as the termination characters.

The TextSerialCom::setTermination method has been updated to take a second parameter returnTermination. If this second parameter is provided, then it will set m_returnTermination. If it is not provided, then m_returnTermination will be set to m_termination (which is the current behavior prior to the changes being introduced in this MR).

Related Issues

• #101 (closed).