Use half-precision for special internal formats.

This change uses half-precision floating-point implementation formats
for all OpenGL half-precision floating-point formats, as well as the
R11F_G11F_B10F and RGB9_E5 special internal formats.

sw::FORMAT_X16B16G16R16F was implemented for the formats without alpha.

RGB9E5 conversion was optimized to not require powf(2.0, x), and 11-
and 10-bit floating-point formats were optimized to map directly to
16-bit half-precision floating-point.

Change-Id: Ic33f903d01f37394244aec9f53b0e67d1c978764
Reviewed-on: https://swiftshader-review.googlesource.com/15410
Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>

src/Renderer/Renderer.cpp

diff --git a/src/Renderer/Renderer.cpp b/src/Renderer/Renderer.cpp
index dbde7e3..aa2038e 100644
--- a/src/Renderer/Renderer.cpp
+++ b/src/Renderer/Renderer.cpp
@@ -281,7 +281,7 @@
 				setupPrimitives = &Renderer::setupPoints;
 			}
 
-			DrawCall *draw = 0;
+			DrawCall *draw = nullptr;
 
 			do
 			{