Add Lucky::CookieJar#[] and #[]=

Adds easier access to cookies by adding the typical key/value syntax
for cookies get/set operations

In the future, this could potentially even implement all of Enumerable({K, V}), but
these methods are super helpful as is to provide hash-like access to cookies

spec/lucky/cookies/cookie_jar_spec.cr

@@ -6,11 +6,15 @@ describe Lucky::CookieJar do
 
     jar.set(:symbol_key, "symbol key")
     jar.set("string_key", "string key")
+    jar[:another_symbol] = "symbol key"
+    jar["another_string"] = "string key"
 
     jar.get(:symbol_key).should eq("symbol key")
     jar.get("symbol_key").should eq("symbol key")
     jar.get("string_key").should eq("string key")
     jar.get(:string_key).should eq("string key")
+    jar[:another_symbol].should eq("symbol key")
+    jar["another_string"].should eq("string key")
   end
 
   it "sets and gets raw HTTP::Cookie object with indifferent access" do

src/lucky/cookies/cookie_jar.cr

@@ -97,6 +97,10 @@ class Lucky::CookieJar
     get?(key) || raise CookieNotFoundError.new(key)
   end
 
+  def [](key)
+    get(key)
+  end
+
   def get?(key : Key) : String?
     cookies[key.to_s]?.try do |cookie|
       decrypt(cookie.value, cookie.name)
@@ -105,10 +109,18 @@ class Lucky::CookieJar
     nil
   end
 
+  def []?(key)
+    get?(key)
+  end
+
   def set(key : Key, value : String) : HTTP::Cookie
     set_raw key, encrypt(value)
   end
 
+  def []=(key, value)
+    set(key, value)
+  end
+
   def set_raw(key : Key, value : String) : HTTP::Cookie
     raw_cookie = HTTP::Cookie.new(
       name: key.to_s,