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/specializer.rb

@@ -1,13 +1,21 @@
 # frozen_string_literal: true
+require 'benchmark'
 
 module Fission
   CODE_PATH = '/userfunc/user'
 
   module Specializer
     def self.call(env)
-      load CODE_PATH
+      request = Request.new(env)
+
+      request.logger.info("Codepath defaulting to #{CODE_PATH}")
+      time = Benchmark.measure { load CODE_PATH }
+      request.logger.info("User code loaded in #{(time.real * 1000).round(3)}ms")
+
       Rack::Response.new([], 201).finish
-    rescue
+
+    rescue => e
+      request.logger.error(%(Specialization failed - #{e}\n#{e.backtrace.join("\n")}))
       Rack::Response.new(['500 Internal Server Error'], 500, {}).finish
     end
   end