feat(frame-rate): add configurable frame-rate option

[TheYahya]

By this changes, we will be able to set frame rate before starting our program.

p := tea.NewProgram(&m, tea.WithAltScreen())
p.FrameRate(time.Second) // setting frame rate to one second
if err := p.Start(); err != nil {
        fmt.Println("Error running program:", err)
        os.Exit(1)
}

fix #577

[meowgorithm]

Related #636

[meowgorithm]

Hi! This doesn't actually solve #636 because it sets a constant framerate as opposed to a max frame rate.

Regardless, if we decide this is something we want to go with with PR will need to:

1. Introduce a ProgramOption for this, i.e. tea.WithFramerate(30)
2. Change variable naming should drop camelcasing to match the variable under the hood: FrameRate -> Framerate
3. Decide if it makes sense for one to be able to change the framerate after the program has started. If so, we'll also want to introduce a command for that so it can be changed from within a program. If not, Program.Framerate should not be exposed.