Add SoundCloud set/playlist support

**Previously:**
Checked the title only for existence of `' by '` in order to match the form `<song name> by <artist name>`

**Problem:**
This did not correctly identify songs in playlists, whose titles have the form `<song name> in <playlist name>`

**Solution:**
Checks for existence of either `' by '` or `' in '`.
Additionally, splits the title at either `by` or `in` in `song()` (same method as in #158 by @oncletom)

Should fix issue #127 ("Scrobbling doesn't work when listening to Soundcloud.com sets").

**Test Cases:**
[Regular case: playlist with song names of format "\<artist name\> - \<song name\>"](https://soundcloud.com/flume/sets/flume-remixes)
-> works great
[Another regular case](https://soundcloud.com/futureclassic/sets/woolfy-city-lights-ep-1)
-> works great
[Album, song names of format "\<song name\>"](https://soundcloud.com/oaklandfalcons/sets/remixxes-vol-3)
-> Doesn't identify artist name because it isn't in song title. User will have to input manually.
-> Possible solution: when this happens, pass the *song title* as the *song name* and pass the *username* as the *artist name*.