Update to v1.0.0, require Ruby 2.3+, added selected demos

simplekit.gemspec

 # -*- ruby -*-
-_VERSION = "0.4.5"
+_VERSION = "1.0.0"
 
 Gem::Specification.new do |s|
   s.name = "simplekit"
   s.version = _VERSION
-  s.date = "2017-12-01"
+  s.date = "2018-07-12"
   s.summary = "Discrete event simulation engine."
   s.homepage = "https://gitlab.nps.edu/pjsanche/simplekit-ruby.git"
   s.email = "pjs@alum.mit.edu"
@@ -14,7 +14,12 @@ Gem::Specification.new do |s|
     simplekit.gemspec
     lib/simplekit.rb
     lib/priority_queue.rb
+    demos/MMk.rb
+    demos/MMk_reference_output.txt
+    demos/MMk_shutdown.rb
+    demos/CancelQ.rb
+    demos/sptf.rb
   ]
-  s.required_ruby_version = '>= 1.8.1'
+  s.required_ruby_version = '>= 2.3.0'
   s.license = 'MIT'
 end