[O] [bug] project publish :auto-postamble and :postamble broken for html

[Eric Schulte]

Hi,

I've noticed that all of my project which either try to set
:auto-postamble to nil, or set a custom value for :postamble have these
settings ignored.

Digging in, in the `org-export-as-html' function, when the project
plists are combined with the infile plists, the :postamble and
:auto-postamble options are removed from the project plist, and a new
:html-postamble option appears.

Through setting the :html-postamble option directly in my project
specification I am able to control the postamble contents on export, so
maybe the fix is as simple as updating the documentation to remove the
:auto-postamble and :postamble options and add the :html-postamble
option, or perhaps (probably preferable) `org-export-as-html' should be
updated to recognize these two options.

Thanks -- Eric