Added nextTip method to fire next tip from code

This came up when i tried to fire the nextTip from code, and had no method to do so.
Also works with tips that are created using nextButton: false within its init options.

its called using $(window).joyride('nextTip'); 
Using class instead of id to identify tour steps

On the documentation says that you can use any ID for the steps container <ol>, but they are not 'displayed none' on the CSS if they are not called #joyRideTipContent
With this you can name your <ol id> differently but attach to them class="joyRideTipContent" so they are not displayed anyway on the html.

Eg.

<ol id="joyRideTour1" class="joyRideTipContent">
<li>Step 1</li>
</ol>

<ol id="joyRideTour2" class="joyRideTipContent">
<li>Step 1</li>
</ol>

<script>
var tourToShow = 1

if (tourToShow == 1){
$("#joyRideTour1").joyride(); 
}else if (tourToShow == 2){
$("#joyRideTour2").joyride(); 
}


</script>
Added top-right nubPosition

Usage:
<ol>
<li data-class="mydataclass" data-options="tipLocation:bottom;nubPosition:top-right">
</li>
</ol>
Merge remote-tracking branch 'upstream/master'
Merge pull request #58 from juliansantaana/master

methods: nextTip, id support for other that 'joyRideTipContent' using class, nubPosition: top-right added