After upgrading the project to XF 1.3.1 the app android app crashes on start up (the iOS app does as well, but I will make a new thread for that).
So it took me a long time to actually get the app to compile and start running, I had to remove and re-add all the packages multiple times.
Here are the packages for my Android project
<package id="ExifLib.PCL" version="1.0.0" targetFramework="MonoAndroid41" />
<package id="modernhttpclient" version="2.1.5" targetFramework="MonoAndroid41" />
<package id="Xamarin.Android.Support.v4" version="21.0.3.0" targetFramework="MonoAndroid41" />
<package id="Xamarin.Android.Support.v7.AppCompat" version="21.0.3.0" targetFramework="MonoAndroid41" />
<package id="Xamarin.Android.Support.v7.MediaRouter" version="21.0.3.0" targetFramework="MonoAndroid41" />
<package id="Xamarin.Forms" version="1.3.1.6296" targetFramework="MonoAndroid41" />
<package id="Xamarin.Forms.Labs" version="1.2.1-pre2" targetFramework="MonoAndroid41" />
<package id="Xamarin.Forms.Maps" version="1.3.1.6296" targetFramework="MonoAndroid41" />
<package id="Xamarin.GooglePlayServices" version="22.0.0.0" targetFramework="MonoAndroid41" />I also had to change the Linker to 'Don't Link', otherwise I would get error :
/Library/Frameworks/Mono.framework/External/xbuild/Xamarin/Android/Xamarin.Android.Common.targets: Error: Error executing task LinkAssemblies: error XA2006: Reference to metadata item 'Android.Gms.Maps.Model.Marker Android.Gms.Maps.GoogleMap/InfoWindowClickEventArgs::get_P0()' (defined in 'Xamarin.Forms.Maps.Android, Version=1.3.1.0, Culture=neutral, PublicKeyToken=null') from 'Xamarin.Forms.Maps.Android, Version=1.3.1.0, Culture=neutral, PublicKeyToken=null' could not be resolved.
I changed the Minimum Android version from 'Override - Android 4.0.3 (API level 15)' to 'Override - Android 4.1 (API level 16)', the Target Android version from 'Override - Android 4.4 (API level 19)' to 'Override - Android 5.0 (API level 21)' and the Target framework form 'Android 4.4' to 'Android 5.0'.
I also did all the standard changes to the App class, AppDelegate and MainActivity.
So the app compiles but while it is starting up I get these messages in the output window
[MonoDroid] UNHANDLED EXCEPTION:
[MonoDroid] System.NullReferenceException: Object reference not set to an instance of an object
[MonoDroid] at Xamarin.Forms.Platform.Android.FormsApplicationActivity.OnDestroy () <IL 0x0002d, 0x000d8>
[MonoDroid] at Android.App.Activity.n_OnDestroy (intptr,intptr) <IL 0x0000a, 0x0009f>
[MonoDroid] at (wrapper dynamic-method) object.8fab5e09-cf4f-4336-985d-83a578b0eefa (intptr,intptr) <IL 0x00011, 0x0003b>
[mono-rt] [ERROR] FATAL UNHANDLED EXCEPTION: System.NullReferenceException: Object reference not set to an instance of an object
[mono-rt] at Xamarin.Forms.Platform.Android.FormsApplicationActivity.OnDestroy () [0x00000] in <filename unknown>:0
[mono-rt] at Android.App.Activity.n_OnDestroy (IntPtr jnienv, IntPtr native__this) [0x00000] in <filename unknown>:0
[mono-rt] at (wrapper dynamic-method) object:8fab5e09-cf4f-4336-985d-83a578b0eefa (intptr,intptr)and then the app crashes.
It would be great if I could get a push in the right direction to try fix this issue 
(hope I have given enough information).