Fix Timeline::isComplete immediately after changes

The endTime is calculated based on the mDuration of this TimelineItem.  If the duration of this TimlineItem instance should be updated, then we should recalculate the duration before using mDuration in the calculation of endTime.
Merge pull request #515 from nhogle/patch-1

Fix Timeline::isComplete immediately after changes
defer throwing exception until IAudioClient::Initialize() fails. Fixes #518.
improve audio::Voice docs
support half-float as an image source texture type
upgrade windows audio test projects to vs 2013
throw exception if hresult from IsFormatSupported() doesn't return a code we think we can handle.
protect against closestMatch leaking if an exception is thrown.
Merge pull request #531 from pizthewiz/half-float

support half-float as an image source texture type
initial Param support for Pan2dNode.
implement sample accurate panning
better test code for Pan2dNode::setStereoInputModeEnabled()
fix reversed panning positions in FallingGears sample
Added Timeline::applyAt and removeTargetAt() to allow for ‘delayed apply’ Tweens.
added audio::Param::Options::beginTime()
make FilePlayerNode::stop(), seek() callable from the audio thread
Fixed bug in SamplePlayerNode when it was default constructed and its ChannelMode wasn’t correctly set. Clarify ChannelModes for InputNode and SamplePlayerNode.
Remove disable() / enable() when setting Buffer, it isn’t needed since we hold the lock.
removed default true from Node and Context setEnabled(), use enable() instead
added timeToFrame() util function