Move footer content into template

This caused problems because liquid >=3.0.0 does not allow a
variable and a template with the same name. Here we had a
variable and a template both called footer.

docs/site.yml

@@ -7,12 +7,3 @@
 jq_version: "1.4-2-g15c4a7f-dirty"
 
 root: '/jq'
-footer: |
-
-  This website is made with [Bonsai](http://www.tinytree.info) and
-  [Bootstrap](http://getbootstrap.com), themed
-  with [Bootswatch](https://bootswatch.com).
-
-  jq is licensed under the MIT license (code) and the
-  [CC-BY-3.0](https://creativecommons.org/licenses/by/3.0/) license
-  (docs).