Enhance readability of error messages for GLSL

Specifically, make GLSL link error messages more specific and output
only information relevant to the error.

Also change type printing to more closely reflect GLSL syntax. This
is the default for link error messages, but must me enabled with the
new option --enhanced-msgs for compilation error messages.

Also with --enhanced-msgs, only emit one error message per source
line.

Test/enhanced.7.frag

@@ -0,0 +1,20 @@
+#version 450 core
+
+layout (location = 0) out vec4 FragColor;
+
+layout (location = 0) in Vertex
+{
+        vec4 color;
+        vec3 worldSpacePos;
+        vec3 worldSpaceNorm;
+        vec2 texCoord1;
+        flat int cameraIndex;
+} fs_in;
+
+layout (binding = 1) uniform sampler2D t0;
+
+void main()
+{             
+    FragColor = texture(t0, fs_in.texCoord1);   
+}
+