Add Logo (#113)

* Add Logo

* Add Logo to readme

* fix max size of logo in readme

* fix max size of logo in readme

* fix max size of logo in readme

* fix width in readme

Author: oxinabox

README.md

@@ -1,3 +1,5 @@
+<img src="docs/src/assets/logo.svg" width="256"/>
+
 # ChainRules
 
 [![Travis](https://travis-ci.org/JuliaDiff/ChainRules.jl.svg?branch=master)](https://travis-ci.org/JuliaDiff/ChainRules.jl)

docs/src/assets/logo.svg

@@ -0,0 +1,83 @@
+using Pkg: @pkg_str
+# For reproducability only dependency this has is Luxor,
+# and it was created with Luxor v1.6.0
+pkg"add Luxor@v1.6"
+
+using Luxor
+using Random
+
+const bridge_len = 50
+
+function chain(jiggle=0)
+    shaky_rotate(θ) = rotate(θ + jiggle*(rand()-0.5))
+    
+    ### 1
+    shaky_rotate(0)
+    sethue(Luxor.julia_red)
+    link()
+    m1 = getmatrix()
+    
+    
+    ### 2
+    sethue(Luxor.julia_green)
+    translate(-50, 130);
+    shaky_rotate(π/3); 
+    link()
+    m2 = getmatrix()
+    
+    setmatrix(m1)
+    sethue(Luxor.julia_red)
+    overlap(-1.3π)
+    setmatrix(m2)
+    
+    ### 3
+    shaky_rotate(-π/3);
+    translate(-120,80);
+    sethue(Luxor.julia_purple)
+    link()
+    
+    setmatrix(m2)
+    setcolor(Luxor.julia_green)
+    overlap(-1.5π)
+end
+
+
+function link()
+    sector(50, 90, π, 0, :fill)
+    sector(Point(0, bridge_len), 50, 90, 0, -π, :fill)
+    
+    
+    rect(50,-3,40, bridge_len+6, :fill)
+    rect(-50-40,-3,40, bridge_len+6, :fill)
+    
+    sethue("black")
+    move(Point(-50, bridge_len))
+    arc(Point(0,0), 50, π, 0, :stoke)
+    arc(Point(0, bridge_len), 50, 0, -π, :stroke)
+    
+    move(Point(-90, bridge_len))
+    arc(Point(0,0), 90, π, 0, :stoke)
+    arc(Point(0, bridge_len), 90, 0, -π, :stroke)
+    strokepath()
+end
+
+function overlap(ang_end)
+    sector(Point(0, bridge_len), 50, 90, -0., ang_end, :fill)
+    sethue("black")
+    arc(Point(0, bridge_len), 50, 0, ang_end, :stoke)
+    move(Point(90, bridge_len))
+    arc(Point(0, bridge_len), 90, 0, ang_end, :stoke)
+
+    strokepath()
+end
+
+####################
+# Actually draw it
+
+Random.seed!(16)
+Drawing(450,450, "logo.svg")
+origin()
+translate(50, -130);
+chain(0.5)
+finish()
+preview()