rename copyright to footer, since the variable copyright is used in the RSS feed

exampleSite/config.toml

@@ -33,4 +33,4 @@ footnotereturnlinkcontents = "↩"
 
 [params]
     description = "A website built through Hugo and blogdown."
-    copyright = "© [Yihui Xie](https://yihui.name) 2017 | [Github](https://github.com/yihui) | [Twitter](https://twitter.com/xieyihui)"
+    footer = "© [Yihui Xie](https://yihui.name) 2017 | [Github](https://github.com/yihui) | [Twitter](https://twitter.com/xieyihui)"

exampleSite/content/about.md

@@ -43,11 +43,11 @@ You can define the menu through `menu.main`, e.g.,
 
 Alternatively, you can add `menu: main` to the YAML metadata of any of your pages, so that these pages will appear in the menu.
 
-The page footer can be defined in `.Params.copyright`, and the text is treated as Markdown, e.g.,
+The page footer can be defined in `.Params.footer`, and the text is treated as Markdown, e.g.,
 
 ```
 [params]
-    copyright = "© [Yihui Xie](https://yihui.name) 2017"
+    footer = "© [Yihui Xie](https://yihui.name) 2017"
 ```
 
 # Custom layouts

layouts/partials/footer.html

@@ -1,6 +1,6 @@
   <footer>
   {{ partial "foot_custom.html" . }}
-  {{ with .Site.Params.copyright }}
+  {{ with .Site.Params.footer }}
   <hr/>
   {{ . | markdownify }}
   {{ end }}