Recognize missing poppler header.

* README.org:Give more info on poppler-private header. Fixed some typos.

* configure.ac: Added check for poppler private header.
Fixed include directives.

* src/poppler-hack.cc:Use proper header names in includes.
Added license files.
Updated copyright.
Fixed comment style.

* src/epdfinfo.c:Fixed comment style.
Remove outdated comments.

* src/epdfinfo.c:Remove comments about unsupported poppler versions.