support xml:lang in release notes

[maxkadushkin]

following #35, implemented using xml:lang for multilingual releaseNotesLink. language isn't got from OS (need to do it?), but set up by win_sparkle_set_lang. the order of releaseNotesLink items doesn't matter. will be taken the first item without xml:lang tag and the last with suitable language

[vslavik]

Thanks for your PR! I can’t merge it in its current state, unfortunately, could you please polish it per the inline comments I’ll add in a moment? I’d also appreciate better commit message with accurate title (#35’s one is more meaningful and understandable than the one you used; there’s nothing “dependent” there for one thing) and a description (the caveats about how it behaves present in this PR should be part of the commit message — see http://chris.beams.io/posts/git-commit/ for the rationale.)

[maxkadushkin]

yes, of course, I'll examine my changes accordigly your comments

[vslavik]

Merge with upstream

This makes merging the PR somewhat messy :( To reiterate, I'd be happy to merge this once the bugs are fixed.

[maxkadushkin]

yes, of course. i have no PR without changes according your remarks

[vslavik]

So much for your promise in 2016… or the spirit of contributing back :(