Updated to libwebp 0.4.0 and added basic unit test project
Fixes to libwebp .40 update

Changes unit test project to xunit and net 2.0.
Reduces unit test image size.
I release these contributions under the terms of the Imazen Contributor
Agreement V1.0
(http://imageresizing.net/licenses/contribute), the terms of which I
accept and agree.
- Matt Abboud 6/16/2014

Fixed test project (Had 4.5 refs but was 2.0)
Replaced native binaries with .dlls built from 0.4.0 branch.