Misc distribution udpates

Hi, I've introduced some minor changes:
* `Changes` file now satisfies `CPAN::Changes::Spec`. There is a special [online service to check your CPAN uploads](http://changes.cpanhq.org/author/TMHARISH) for correctness of the changelog.
* Link to this repository was added to the Makefile.PL, so that it could be displayed nicely on [MetaCPAN](https://metacpan.org/release/Net-XMPP-Client-GTalk).
* Indirect syntax for constructors was substituted for a safer version. You can read on why indirect object notation is bad [here](https://stackoverflow.com/questions/429657/what-is-the-difference-between-new-someclass-and-someclass-new-in-perl) and [here](http://shadow.cat/blog/matt-s-trout/indirect-but-still-fatal/).

Cheers,
Sergey.