Update babylon.skeleton.ts
Update babylon.skeleton.ts

I handed over the functions as before and have added another that better suits what I wanted to do.
This allows you to:
```
var hant_left = skeleton.searchIndexOnSkeletonByName("hant_left");
sword.attachToBone(skeleton.bones[hant_left], character);
```
It is easier to give a bone name as an index for attachToBone
NicolasBuecher/Babylon.js,Kesshi/Babylon.js,Kesshi/Babylon.js,NicolasBuecher/Babylon.js,jbousquie/Babylon.js,Temechon/Babylon.js,sebavan/Babylon.js,Hersir88/Babylon.js,BabylonJS/Babylon.js,jbousquie/Babylon.js,NicolasBuecher/Babylon.js,RaananW/Babylon.js,RaananW/Babylon.js,jbousquie/Babylon.js,Hersir88/Babylon.js,Hersir88/Babylon.js,Kesshi/Babylon.js,Temechon/Babylon.js,BabylonJS/Babylon.js,abow/Babylon.js,RaananW/Babylon.js,Temechon/Babylon.js,sebavan/Babylon.js,abow/Babylon.js,abow/Babylon.js,BabylonJS/Babylon.js,sebavan/Babylon.js