Removal of logChange method and explanation

logChange is an example of an extension, not part of the standard library. To add extensions, simply extend the interface outside of the definition file:

interface KnockoutExtenders {
    logChange(target: KnockoutObservableAny, option: string): KnockoutObservableAny;
}
Merge pull request #402 from Steve-Fenton/patch-3

Removal of logChange method and explanation