Add a TypeScript definition for Enumerable.from method

[noy-shimotsuki]

If type is 'any', code completion does not work, and typo does not cause compilation error, so it is desirable to avoid the 'any' type as much as possible.

Add 'Enumerable.from(obj: { [key: string]: T }): IEnumerable<{ key: string; value: T }>' as definition, the method will return the good type even when the parameter is a hash-like object.

[mihaifm]

Thanks for these changes and for the detailed explanations.