resolves #448 decode character references in link URIs (PR #450)
resolves #448 decode character references in link URIs (PR #450)

- decode character references (e.g., &amp;) in link URIs
- update terminology for refering to character references
- minor code cleanups
mojavelinux/asciidoctor-pdf,Hextremist/asciidoctor-pdf,Hextremist/asciidoctor-pdf,asciidoctor/asciidoctor-pdf,mojavelinux/asciidoctor-pdf,dsisnero/asciidoctor-pdf,dsisnero/asciidoctor-pdf,asciidoctor/asciidoctor-pdf