Correct initialisms as suggested by golint

Correct initialisms as suggested by golint

First step to use initialisms that golint suggests,
for example:

    Line 116: func GetHtmlRenderer should be GetHTMLRenderer

as see on http://goreportcard.com/report/spf13/hugo

Thanks to @bep for the idea!

Note that command-line flags (cobra and pflag)
as well as struct fields like .BaseUrl and .Url
that are used in Go HTML templates need more work
to maintain backward-compatibility, and thus
are NOT yet dealt with in this commit.

First step in fixing #959.