add edge drawing, stereographic geometry shader for handling curved projections

vis/shaders/stereo-proper.vs.glsl

@@ -0,0 +1,12 @@
+#version 430
+
+layout(location=1) uniform mat4 view;
+
+layout(location=0) in vec4 pos;
+
+out vec4 gpos;
+
+void main() {
+    gpos = view * pos;
+    gl_PointSize = 5;
+}