function Presentation(baseURL, slides) {
	this.baseURL = baseURL;
	this.slides = slides;
	this.index = 0;
	this.LoadSlide();
}
Presentation.prototype.LoadSlide = function () {
	document.getElementById('slide_txt').innerHTML = slides[this.index].alt;
	document.getElementById('slide_img').src = this.baseURL + slides[this.index].img;
}
Presentation.prototype.Next = function () {
	if(this.index < (this.slides.length - 1)) {
		this.index++;
		this.LoadSlide();
	}
}
Presentation.prototype.Previous = function () {
	if(this.index > 0) {
		this.index--;
		this.LoadSlide();
	}
}