hugolib: Do not tolower result from Page.GetParam

We still do lowering of the param strings in some internal use of this, but the exported `GetParam` method is changed to a more sensible default.

This was used for the `disqus_title` etc. in the internal Disqus template, which was obviously not right.

If you really want to lowercase your params, do it with `.GetParam "myparam" | lower` or similar.

Fixes #4187

hugolib/site.go

@@ -1451,7 +1451,7 @@ func (s *Site) assembleTaxonomies() {
 
 		for _, p := range s.Pages {
 			vals := p.getParam(plural, !s.Info.preserveTaxonomyNames)
-			weight := p.GetParam(plural + "_weight")
+			weight := p.getParamToLower(plural + "_weight")
 			if weight == nil {
 				weight = 0
 			}