Add URHO3D_API to BufferedSoundStream. [ci skip]
Replace plist particle file with Staring extension particle system (pex).
Add greenspiral particle file.[ci skip]
Simplify sound stream code and improve the SoundSynthesis sample. Closes #257.
Added documentation for the sound streaming feature.
Merge remote-tracking branch 'upstream/master'

Conflicts:
	Bin/Data/LuaScripts/25_Urho2DParticle.lua
	Bin/Data/Scripts/25_Urho2DParticle.as
	Source/Samples/25_Urho2DParticle/Urho2DParticle.cpp
	Source/Samples/29_SoundSynthesis/SoundSynthesis.cpp
	Source/Samples/29_SoundSynthesis/SoundSynthesis.h