Obtaining the version of an installed package

[Bozhidar Batsov]

Hey everyone, 

I'm wondering if there's an API for obtaining metadata about installed packages, in particular the version information.

For years I was using this function from pkg-info https://github.com/emacsorphanage/pkg-info/blob/master/pkg-info.el#L65, but I'm wondering if it'd be easy to strip one dependency from my packages. 

I've skimmed over package.el, but I didn't notice anything that does this, that's why I decided to ask on the mailing list as well.

I see there's the function `package-get-descriptor`, but it seems it was added only 7 months ago, so it can't be used in packages that need to support several Emacs versions. Copying it and related functions might work, but I'm hoping to find a more elegant solution. Thanks in advance for your help!