Add configuration option for ghost reset distance. Improve documentation.

textshader.glsl

@@ -1,4 +1,5 @@
 #version 460 core
+// HUD text vertex shader: projects screen-space quad verts and forwards glyph UVs.
 layout (location = 0) in vec4 vertex; // <vec2 pos, vec2 tex>
 out vec2 TexCoords;