ox-html: Support more programming languages in CSS

* lisp/ox-html.el (org-html-style-default): Add languages.

The standard CSS for HTML export only supported a couple of
programming languages to have a language name "hover" on src
blocks.  This patch adds all languages supported per Org
manual, those from org.el's org-babel-load-languages-alist,
additional language identifiers in ob-*.el and languages
which have a) an emacs mode and b) are supported by the LaTeX
listings package.  Additional a language "conf" is supported
for generic configuraiton files; an emacs mode exists for
this, but for LaTeX listings a language " " has to be faked.
As this patch is for HTML, this is no impediment.

Thanks for reporting the missing support to Tianxian XIONG.

lisp/ox-html.el

@@ -320,13 +320,96 @@ for the JavaScript code in this tag.
     border: 1px solid black;
   }
   pre.src:hover:before { display: inline;}
-  pre.src-sh:before    { content: 'sh'; }
-  pre.src-bash:before  { content: 'sh'; }
+  /* Languages per Org manual */
+  pre.src-asymptote:before { content: 'Asymptote'; }
+  pre.src-awk:before { content: 'Awk'; }
+  pre.src-C:before { content: 'C'; }
+  /* pre.src-C++ doesn't work in CSS */
+  pre.src-clojure:before { content: 'Clojure'; }
+  pre.src-css:before { content: 'CSS'; }
+  pre.src-D:before { content: 'D'; }
+  pre.src-ditaa:before { content: 'ditaa'; }
+  pre.src-dot:before { content: 'Graphviz'; }
+  pre.src-calc:before { content: 'Emacs Calc'; }
   pre.src-emacs-lisp:before { content: 'Emacs Lisp'; }
-  pre.src-R:before     { content: 'R'; }
-  pre.src-perl:before  { content: 'Perl'; }
-  pre.src-java:before  { content: 'Java'; }
-  pre.src-sql:before   { content: 'SQL'; }
+  pre.src-fortran:before { content: 'Fortran'; }
+  pre.src-gnuplot:before { content: 'gnuplot'; }
+  pre.src-haskell:before { content: 'Haskell'; }
+  pre.src-java:before { content: 'Java'; }
+  pre.src-js:before { content: 'Javascript'; }
+  pre.src-latex:before { content: 'LaTeX'; }
+  pre.src-ledger:before { content: 'Ledger'; }
+  pre.src-lisp:before { content: 'Lisp'; }
+  pre.src-lilypond:before { content: 'Lilypond'; }
+  pre.src-matlab:before { content: 'MATLAB'; }
+  pre.src-mscgen:before { content: 'Mscgen'; }
+  pre.src-ocaml:before { content: 'Objective Caml'; }
+  pre.src-octave:before { content: 'Octave'; }
+  pre.src-org:before { content: 'Org mode'; }
+  pre.src-oz:before { content: 'OZ'; }
+  pre.src-plantuml:before { content: 'Plantuml'; }
+  pre.src-processing:before { content: 'Processing.js'; }
+  pre.src-python:before { content: 'Python'; }
+  pre.src-R:before { content: 'R'; }
+  pre.src-ruby:before { content: 'Ruby'; }
+  pre.src-sass:before { content: 'Sass'; }
+  pre.src-scheme:before { content: 'Scheme'; }
+  pre.src-screen:before { content: 'Gnu Screen'; }
+  pre.src-sed:before { content: 'Sed'; }
+  pre.src-sh:before { content: 'shell'; }
+  pre.src-sql:before { content: 'SQL'; }
+  pre.src-sqlite:before { content: 'SQLite'; }
+  /* additional languages in org.el's org-babel-load-languages alist */
+  pre.src-forth:before { content: 'Forth'; }
+  pre.src-io:before { content: 'IO'; }
+  pre.src-J:before { content: 'J'; }
+  pre.src-makefile:before { content: 'Makefile'; }
+  pre.src-maxima:before { content: 'Maxima'; }
+  pre.src-perl:before { content: 'Perl'; }
+  pre.src-picolisp:before { content: 'Pico Lisp'; }
+  pre.src-scala:before { content: 'Scala'; }
+  pre.src-shell:before { content: 'Shell Script'; }
+  pre.src-ebnf2ps:before { content: 'ebfn2ps'; }
+  /* additional language identifiers per \"defun org-babel-execute\"
+       in ob-*.el */
+  pre.src-cpp:before  { content: 'C++'; }
+  pre.src-abc:before  { content: 'ABC'; }
+  pre.src-coq:before  { content: 'Coq'; }
+  pre.src-groovy:before  { content: 'Groovy'; }
+  /* additional language identifiers from org-babel-shell-names in
+     ob-shell.el: ob-shell is the only babel language using a lambda to put
+     the execution function name together. */
+  pre.src-bash:before  { content: 'bash'; }
+  pre.src-csh:before  { content: 'csh'; }
+  pre.src-ash:before  { content: 'ash'; }
+  pre.src-dash:before  { content: 'dash'; }
+  pre.src-ksh:before  { content: 'ksh'; }
+  pre.src-mksh:before  { content: 'mksh'; }
+  pre.src-posh:before  { content: 'posh'; }
+  /* Additional Emacs modes also supported by the LaTeX listings package */
+  pre.src-ada:before { content: 'Ada'; }
+  pre.src-asm:before { content: 'Assembler'; }
+  pre.src-caml:before { content: 'Caml'; }
+  pre.src-delphi:before { content: 'Delphi'; }
+  pre.src-html:before { content: 'HTML'; }
+  pre.src-idl:before { content: 'IDL'; }
+  pre.src-mercury:before { content: 'Mercury'; }
+  pre.src-metapost:before { content: 'MetaPost'; }
+  pre.src-modula-2:before { content: 'Modula-2'; }
+  pre.src-pascal:before { content: 'Pascal'; }
+  pre.src-ps:before { content: 'PostScript'; }
+  pre.src-prolog:before { content: 'Prolog'; }
+  pre.src-simula:before { content: 'Simula'; }
+  pre.src-tcl:before { content: 'tcl'; }
+  pre.src-tex:before { content: 'TeX'; }
+  pre.src-plain-tex:before { content: 'Plain TeX'; }
+  pre.src-verilog:before { content: 'Verilog'; }
+  pre.src-vhdl:before { content: 'VHDL'; }
+  pre.src-xml:before { content: 'XML'; }
+  pre.src-nxml:before { content: 'XML'; }
+  /* add a generic configuration mode; LaTeX export needs an additional
+     (add-to-list 'org-latex-listings-langs '(conf \" \")) in .emacs */
+  pre.src-conf:before { content: 'Configuration File'; }
 
   table { border-collapse:collapse; }
   caption.t-above { caption-side: top; }