✨ API Request improvements

[benfoxall]

A few things have changed with user.getRecentTracks since I created this.

1. from / to timestamps - would allow regions of a timeline to be filled, and could avoid an edge case where a new song playing could miss a track.
2. limit - seems to support up to 1000 now, could support larger pages (though I did get some errors when I played around with this).
3. json - although it's cool to be using xslt, there's a json endpoint now which might make persistence easier
4. errors - looks like there's some more api errors, maybe some retry and backoff rules would be helpful #28
5. browser storage - it'd be even easier to cache responses.

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idea: maintain a state or regions of data, implement a backfill(user, start, end?) which will update those regions and cache data.