Ability to set Window Flags

[meir]

Changes

• Added WindowFlag enum
• Changed call from (app *App) NewWindow(uint, uint, bool, string) *Window to (app *App) NewWindow(uint, uint, bool, string, WindowFlag) *Window
• Replaced default flags with flags given to a window to the WindowFlag variable given with the NewWindow call

Example

package main

import (
	"github.com/raff/ultralight-go"
)

func main() {
	app := ultralight.NewApp()
	defer app.Destroy()

	window := app.NewWindow(800, 600, false, "Window", ultralight.WindowFlagBorderless | ultralight.WindowFlagResizable)
	defer window.Destroy()

	window.View().LoadURL("file:///assets/index.html")

	window.Focus()
	app.Run()
}

[raff]

Maybe it would be better to add a new constructor (NewWindowWithFlag) or have a DefaultWindowFlags constant set to the current default flags.

[meir]

I've reverted the NewWindow method back to its original state and added the method NewWindowUsingFlags
I have also added an example for the flags as examples/flags.go