GitLab

(doc-view-ghostscript-program, doc-view-dvipdfm-program)
(doc-view-ps2pdf-program): Use executable-find.  Simplify custom type.
(doc-view-ghostscript-options): Improve custom type.
(doc-view-cache-directory, doc-view-conversion-buffer)
(doc-view-conversion-refresh-interval): Simplify custom type.