Add some improvements

[triplem]

• improvement: add several new tags for each album and track
• improvement: add several new tags (e.g. artist_sort, url) to the tracks
• improvement: add possibility to use '/' in dir-property, to allow subdirectory creation (e.g. %ARTIST%/%ALBUM%)
• feature: add possibility to name the first image folder.jpg, so that clients recognize this picture, even though it is not embedded (Issue #12)
• feature: add multi disc support (Issue #14), this does right now just covers the handling of tags (discnumber, discstotal) and does not take care about the filehandling

currently working more on the multi disc handling, probably you would like to wait. but i do like to have some input on the already done stuff. is this going into the right direction? what do you think?

[triplem]

I guess the main functionality for multi-disc support is now done. Some minor issues still remain, like using the subtitle of a disc, if wanted. Furthermore the added functionality should be added to the Changelog.

What do you think? I guess this is a hugh step into the right direction ;-)

[jesseward]

Thanks for submitting this. I will merge a local copy and run through a few tests over the weekend.

[triplem]

The above is now tested and could be merged without any issues. If there is no need from your side, I will go ahead and put these changes into my own master ;-)

Any feedback is appreciated.

[jesseward]

thanks for these. I have merged these changes in, with a few minor changes.