Implement bidirectional serial terminal

[Dan-Kouba]

Description

Currently, the serial commands in the CLI offer monitor, which is a read-only serial connection to the device. It would be very helpful for development if bidirectional communication was implemented in the CLI.

Example

I propose that we replace particle serial monitor with a new serial command particle serial terminal that implements bidirectional communication.

Motivation

In general I believe our tools should be a one-stop-shop for development on our platform, and being able to communicate with my device is a basic requirement for many projects.

Additionally, since Workbench leverages the CLI, developers have to switch to a 3rd party program in order to talk to a device. I think this feels clunky and doesn't make for a great user experience. Workbench should provide all the necessary features for product development, including being able to communicate with my device.