Move shaders into glsl and hlsl directories

Move `data/shaders` to `data/shaders/glsl`
Move `data/hlsl` to `data/shaders/hlsl`

Fix up shader paths in the cpp files to point to the new glsl location.

`data/shaders/hlsl/compile.py` still overwrites the glsl .spv files (for
now).

Issue: #723

data/shaders/glsl/computeparticles/particle.comp

@@ -0,0 +1,76 @@
+#version 450
+
+struct Particle
+{
+	vec2 pos;
+	vec2 vel;
+	vec4 gradientPos;
+};
+
+// Binding 0 : Position storage buffer
+layout(std140, binding = 0) buffer Pos 
+{
+   Particle particles[ ];
+};
+
+layout (local_size_x = 256) in;
+
+layout (binding = 1) uniform UBO 
+{
+	float deltaT;
+	float destX;
+	float destY;
+	int particleCount;
+} ubo;
+
+vec2 attraction(vec2 pos, vec2 attractPos) 
+{
+    vec2 delta = attractPos - pos;
+	const float damp = 0.5;
+    float dDampedDot = dot(delta, delta) + damp;
+    float invDist = 1.0f / sqrt(dDampedDot);
+    float invDistCubed = invDist*invDist*invDist;
+    return delta * invDistCubed * 0.0035;
+}
+
+vec2 repulsion(vec2 pos, vec2 attractPos)
+{
+	vec2 delta = attractPos - pos;
+	float targetDistance = sqrt(dot(delta, delta));
+	return delta * (1.0 / (targetDistance * targetDistance * targetDistance)) * -0.000035;
+}
+
+void main() 
+{
+    // Current SSBO index
+    uint index = gl_GlobalInvocationID.x;
+	// Don't try to write beyond particle count
+    if (index >= ubo.particleCount) 
+		return;	
+
+    // Read position and velocity
+    vec2 vVel = particles[index].vel.xy;
+    vec2 vPos = particles[index].pos.xy;
+
+    vec2 destPos = vec2(ubo.destX, ubo.destY);
+
+    vec2 delta = destPos - vPos;
+    float targetDistance = sqrt(dot(delta, delta));
+    vVel += repulsion(vPos, destPos.xy) * 0.05;
+
+    // Move by velocity
+    vPos += vVel * ubo.deltaT;
+
+    // collide with boundary
+    if ((vPos.x < -1.0) || (vPos.x > 1.0) || (vPos.y < -1.0) || (vPos.y > 1.0))
+    	vVel = (-vVel * 0.1) + attraction(vPos, destPos) * 12;
+    else
+    	particles[index].pos.xy = vPos;
+
+    // Write back
+    particles[index].vel.xy = vVel;
+	particles[index].gradientPos.x += 0.02 * ubo.deltaT;
+	if (particles[index].gradientPos.x > 1.0)
+		particles[index].gradientPos.x -= 1.0;
+}
+