Images and more link types supported

[LinusU]

This includes #28, #30, #31, #32, #33 and #35. If you want to review them separately I think that their commits should disappear from below when you merge them.

The only thing that is relevant to this pull request is faa0197, which depends on the other hence the inclusion.

I've added support for a new type of SpObject, Image. All link functions Image.getFromUrl and img.getUrl is implemented. You can also get an image object form an Album, Artist or Playlist.

Some tab and spaces misses are also fixed.

[LinusU]

While testing my app I have received the following error about two times. I don't think that it has anything to do with this pull request but if you could test out this and notify me if anyone gets it aswell. I have always got the error in the middle of playing a song, while not making any other calls to libspotify.

#
# Fatal error in ../deps/v8/src/api.h, line 297
# CHECK(allow_empty_handle || that != __null) failed
#

[1]    42784 abort      node .

[LinusU]

@Floby Please take a look when you have time!

[LinusU]

@Floby ping! I've updated with a small bugfix...

[Floby]

Sorry I haven't been replying to this pull request. Work leave me no time to review these at the moment but I promise I will make time !

[LinusU]

Ok, thanks!