Fix release date (use microdata date published)
Set default values for packaging, language and script

Most of stuffs imported from Bandcamp is eng/latin, and packaging should be None for digital releases.
Fix up free/paid download links

The matter is quite complex here, as Bandcamp is providing many options for the artist.
Mostly this should fix mixing up free download / paid download links in almost all cases.
Merge pull request #20 from zas/bandcamp_fixes

Bandcamp fixes