Extend ob-maxima: add input variables and graphic output
* lisp/ob-maxima.el (org-babel-tangle-lang-exts): Maxima extension.
(org-babel-maxima-expand): Add input variables and graphic output.
(org-babel-execute:maxima): Add input variables and graphic output.
(org-babel-maxima-var-to-maxima): Add input variables and graphic
output.
(org-babel-maxima-graphical-output-file): Add input variables and
graphic output.
(org-babel-maxima-elisp-to-maxima): Add input variables and graphic
output.
* testing/examples/ob-maxima-test.org: Examples for new Maxima
behavior.