Added support to extension methods

[ZverGuy]

For now extension methods can be called from js code

[ackava]

This will slow down startup and create unnecessary extensions of every type in C#. And generic extensions will not work.

Again, this doesn't have to be part of YantraJS.

What we can do is, we can setup some sort of events that will be raised when a new ClrType is being created. So in your own code (may be a separate extension), you can setup your logic to add extensions.