Adding getObject that retrives data using Gson's TypeToken

[Megamiun]

Hello,

I really loved your library, it helped me testing some features in my prototype.

But, using maps in Kotlin, I had some difficulties trying to get the map automatically filled. After some time trying to make things work, I remembered that Gson has a TypeToken interface that solved cases like that.

Originally I did this as an issue on mukeshsolanki/easypreferences#4, but I thought it would be correct to share this change with your project too as it served as a basis for him, so I will make a PR for it.