Add support for int on PropertyCollection

[IchimakiKasura]

Just found this cool ini-parser but I've encountered little problem while working on my project. On the single Section I have many properties which by the way has long names.

So my PR would be adding an INT or Numbers support to look like this Which is also can be used when using a Loop when having too many properties on a section.

I hope my code changes helps!

[IchimakiKasura]

Also added automatic return type and fixed my mistakes on the first commit because it was only returning the KeyName and not the KeyValue

So that it no longer requires int.Parse because it automatically does it.