(v2) Proposal: program execution flow

[aymanbagabas]

Currently, Bubble Tea programs has the following methods to start and run a program.

• Start() error starts the program and waits without returning a final model deprecated
• Run() (Model, error) starts the program and waits
• Wait() waits for the program to finish (the aforementioned ones already wait for the program to exit, this is redundant)
• Kill() kills the program (currently it only cancels the context) Related issues: Recover panics from within cmds goroutines #234 After a panic() the terminal input does not show #1127

To keep the API similar to other Go packages, we could change the API to be as follows:

• Start() error starts the program and event loop
• Wait() error waits for the event loop to finish and exit
• Run() error becomes a helper that starts and waits for the program
• Kill() error kills the program and forces the event loop to stop

With this, we would expose a program.Model that has the final model after the program exits. During the lifetime of the program, program.Model would be nil. This is similar to the exec.Cmd API in the standard library.