Add exercise: hello world (JuliaLang#13)

* Add exercise: hello world

* hello-world: Remove unicode test & improve topics

config.json

@@ -5,6 +5,14 @@
   "active": false,
   "test_pattern": "TODO",
   "exercises": [
+    {
+      "slug": "hello-world",
+      "difficulty": 1,
+      "topics": [
+        "strings",
+        "string interpolation"
+      ]
+    },
     {
       "slug": "hamming",
       "difficulty": 1,

exercises/hello-world/example.jl

@@ -0,0 +1,3 @@
+function hello(name::AbstractString="World")
+    return "Hello, $(name)!"
+end

exercises/hello-world/hello-world.jl

@@ -0,0 +1,3 @@
+function hello()
+
+end

exercises/hello-world/runtests.jl

@@ -0,0 +1,12 @@
+using Base.Test
+
+include("hello-world.jl")
+
+@testset "no name" begin
+    @test hello() == "Hello, World!"
+end
+
+@testset "names" begin
+    @test hello("Alice") == "Hello, Alice!"
+    @test hello("Bob") == "Hello, Bob!"
+end