add drawPoint/drawLine (both slow) and drawPoints (faster) to GLInstancingRenderer, with GLSL shaders

btgui/OpenGLWindow/Shaders/linesPS.h

@@ -0,0 +1,10 @@
+//this file is autogenerated using stringify.bat (premake --stringify) in the build folder of this project
+static const char* linesFragmentShader= \
+"#version 150\n"
+"in vec4 colourV;\n"
+"out vec4 fragColour;\n"
+"void main(void)\n"
+"{\n"
+"    fragColour = colourV;\n"
+"}\n"
+;