Add new backgrounds (#764)

* Add quark background

* add galaxy background

parts/backgrounds/galaxy.lua

@@ -0,0 +1,43 @@
+--Space with stars
+local gc=love.graphics
+local circle,setColor,hsv=gc.circle,gc.setColor,COLOR.hsv
+local rnd,pi,sin,cos=math.random,math.pi,math.sin,math.cos
+local back={}
+
+local sDist,sRev={},{} -- star data in SoA [distance from center, revolution progress, color]
+local k
+
+local d,r -- temp vars for optimization
+function back.init()
+    if sDist[1]then return end
+    local max
+    for i=0,20 do
+        max=16*(i+1)
+        for j=1,max do
+            sDist[#sDist+1]=i+rnd()
+            sRev[#sRev+1]=2*pi*j/max+2*pi*rnd()/max
+        end
+    end
+end
+function back.resize(w,h)k=3*SCR.k end
+function back.update(dt)
+    for i=1,#sDist do sRev[i]=(sRev[i]+dt/(sDist[i]+1))%(2*pi) end
+end
+function back.draw()
+    gc.clear()
+    gc.translate(SCR.cx,SCR.cy)
+    gc.rotate(1)
+    for i=1,#sDist do
+        d,r=sDist[i],sRev[i]
+        if d<5 then
+            setColor(hsv(.088,(d-2)/7,1,.7))
+        else
+            setColor(hsv(.572,d/70+.1,(22-d)/12,.7))
+        end
+        circle('fill',8*d*cos(r),24*d*sin(r),3)
+    end
+    gc.rotate(-1)
+    gc.translate(-SCR.cx,-SCR.cy)
+end
+function back.discard()end
+return back