Remove unnecessary files from website

There's a really old params.json that seems to be how the original
website was generated but since completely useless. Just remove it.
Also, set up _config.yaml so that README.md, LICENSE etc won't become
part of the website build.

Author: ychin

_config.yml

@@ -0,0 +1,7 @@
+exclude:
+  - CNAME
+  - Gemfile
+  - Gemfile.lock
+  - LICENSE
+  - README.md
+  - vendor