Add subpixel-aligned supersampling to Rift shader

Do 4 samples per screen pixel, offset the sample origins by the
underlying subpixel positions.  In black vs white areas, this should
give greater horizontal resolution, but any miscorrected chromatic
aberration error will reduce the effect.  This also helps the chromatic
aberration correction work more accurately.

Supersampling helps a lot on its own, because the edges of the barrel
distortion are undersampled as is, and because in virieo we have 2x the
horizontal resolution to sample from (we sample from full screens rather
than half screens).

Shader will work ok when using higher/lower resolutions. It won't be
optimal with Dev Kit v2, but we should be able to do similar sampling,
taking pentile and higher resolution into account in the future.
Fix up subpixel rendering origins

Slightly change the subpixel sampling calculation,
each subpixel is actually equally spaced apart.
Remove incorrect comment about subpixel alignment
Rift Up Changes
IPD Adjuster Figure
Merge pull request #35 from sigboe/master

Update README with new links
Merge pull request #34 from muchcharles/subpixel_supersample

Add subpixel-aligned supersampling to Rift shader
Added RIftUp to the Perception Stereo Mode Select

Made the HMDIsplayInfo class abstract and created a HMDisplayInfo
factory to create the appropriate type depending on the selection in
Perception. Easily extendable for future HMDs (DK2 etc).
Merge of Rift Up Branch in Master
Fixed merge issues from RiftUp branch merge

Fixed a couple of issues introduced as part of the RiftUp branch merge.
Added minimum distortion scale appropriate for each HMD.
VR Mouse Toggle
Merge branch 'master' of https://github.com/cybereality/Perception
Added dependencies to debug DxProxy project
Merge pull request #1 from cybereality/master

Update