switch to kramdown and jekyll 3

Gemfile

@@ -1,2 +1,2 @@
 source 'https://rubygems.org'
-gem 'github-pages'
+gem 'github-pages', group: :jekyll_plugins

_config.yml

@@ -1,8 +1,5 @@
 safe: true
 source: .
-markdown: redcarpet
-redcarpet:
-  extensions: ["smart", "tables", "no_intra_emphasis", "fenced_code_blocks", "autolink", "strikethrough", "superscript", "with_toc_data"]
 
 title: KPD
 
@@ -13,4 +10,5 @@ defaults:
       type: "posts"
     values:
       layout: "post"
-      author: "Kyle P. Davis"
+      author: "Kyle P. Davis"
+