Ruby logger (#251)

* Add logger for ruby environment

* Update readme and example for ruby logger

* ruby-env: log load time for user code

environments/ruby/fission/handler.rb

@@ -5,14 +5,18 @@ require_relative 'context'
 module Fission
   module Handler
     def self.call(env)
+      context = Context.new(env)
+
       response = if method(:handler).arity > 0
-        handler(Context.new(env))
+        handler(context)
       else
         handler
       end
 
       response.is_a?(Array) ? response : Rack::Response.new([response]).finish
-    rescue
+
+    rescue => e
+      context.logger.error(%(Function failed - #{e}\n#{e.backtrace.join("\n")}))
       Rack::Response.new(['500 Internal Server Error'], 500, {}).finish
     end
   end