Fixes disappearing SoundEffects on iOS (#1123)
This is accomplished by manually setting the buffer properties if the packet does not decode (MonoTouch bug)

Fixed broken sound buffer debug output
Fixed MGFX parser to support +/- numbers in sampler and render state values.
Follow XDG Spec and Application Data on Mac/Linux.
IsNullOrEmpty seems fine.
Merge pull request #1671 from flibitijibibo/savedgamesunix

Follow XDG Spec and Application Data on Mac/Linux.
Merge pull request #1659 from SickheadGames/mgfx

Support For Signed Numbers in MGFX
Merge pull request #1630 from Nezz/ios_soundeffect

Fixes disappearing SoundEffects on iOS
Merge branch 'develop' of https://github.com/mono/MonoGame into develop