Add version number to __init__.py and maybe tags/releases

[lipis]

It would be nice to know what's the latest stable or experimental release. I'm including gae_mini_profiler in one of my projects (http://debug.gae-init.appspot.com) and it would be nice to know which version is included if something is wrong or not. Also it's very useful for updates..

[benjaminjkraft]

I think it's more or less always the case that master is what we're using in production, so it should be fairly stable. But it might still be worth us doing releases -- for example it would help with the issue in #74 where we want to make a breaking change.