doc: add 1.5.1

doc: 1.5 release with go modules

release 1.4.1

Merge pull request PuerkitoBio#247 from PuerkitoBio/wip-deprecate

Deprecate NewDocument and NewDocumentFromResponse. Closes PuerkitoBio#173 .

Merge pull request PuerkitoBio#234 from PuerkitoBio/wip-slice-end

Add ToEnd constant to use as special end index in Slice, closes PuerkitoBio#232.

update changelog

Merge branch 'glebtv-setHtml'

Update README.md

add go1.7 to travis