iOS: Peak file now generating in background when a song starts playing.
PeakFile.cs has been renamed to PeakFileGenerator.cs and is no longer dependent on System.Reactive.
Added Normalizer class to MPfm.Core.

Related to issue #323 and issue #405.
iOS: WaveFormView now displays a wave form! 
Still lots of work to do though, but it doesn't seem to create a memory leak yet.
Bug fixes to PeakFileGenerator and PlayerPresenter.

Related to issue #361 and issue #405.