Add final features

[skippyr]

I've finally decided that Teco will be a macOS-specific framework that will support both line-oriented and screen-oriented apps, but only a limited set of terminal events, on its own way.

This issue tracks the addition of the final features I plan to add to the framework, which were previously being discussed in #17, #15, and #4.

Furthermore, I am already rewriting the documentation to be fully integrated within Xcode (#21).

Those features are:

// Cursor Manipulation Functions
// Moves the cursor to a specific coordinate.
try! Terminal.moveCursor(to: .init(column: 0, row: 0))
try! Terminal.moveCursor(column: 0, row: 0)

// Moves the cursor in a direction by a given number of steps.
try! Terminal.moveCursor(.right, by: 5)

// Obtains the current cursor coordinate.
let cursorCoordinate = try! Terminal.cursorCoordinate
Terminal.print("Cursor Coordinate: (column: \(cursorCoordinate.column), row: \(cursorCoordinate.row))")

// ---

// Signal Handling Function
// Sets the given signal handler, possibly injecting code to reset active terminal properties.
Terminal.attachSignalHandler(for: .sigint) {
    Terminal.print("Interrupt Signal")
}

// ---

// Event Reading Functions (only for screen resize and key events)
// Clear cached events from the input buffer.
Terminal.clearEventQueue()

// Pulls the next cached key event.
// Screen resize events are errors that need to be catched, so you don't need to unwrap an enum to filter keys.
Terminal.print("Press \("[Escape]".red.bold) to cancel...")
do {
    let key = try Terminal.pullKeyEvent(waitFor: .seconds(2)) { $0 == .escape }
    guard key == nil else {
        Terminal.print("Operation Cancelled".red, via: .error)
    }
} catch Terminal.Error.screenResizeInterrupt {
    Terminal.print("Screen has been resized. Redrawing interface...")
} catch Terminal.Error.timerElapsed {
    Terminal.print("Timer has been elapsed. Continuing operation.")
}

// ---
// Convenient Input Functions
// Default values are optionals.

// Reads a line of input, similar to Swift's readLine function.
// Outputs: What is the name of your project? (default: My Project)
_ = try! Terminal.readLineQuestion("What is the name of your project?", default: "My Project")
// Reads the "Y" or "N" key input.
// Outputs: Do you want to proceed with the installation? (Y/n)
_ = try! Terminal.readYesOrNoQuestion("Do you want to proceed with the installation?", default: true)