symbol and function markup

[nicferrier]

See #17 - we've done quite a bit already.

Marking up variables and functions is possible on current oddmuse. It's necessary for elwiki to have that... but it also would be useful for many other creole use cases, elwikidoc for example.

Ideas:

[[emacs-variable:buffer-file-name]]
[[emacs-function:get-buffer]]

and we could use a resolver to link them to documentation.

Or we could support the syntax oddmuse has:

`symbol-name'

Not sure how it differentiates between functions and symbols, I don't think it does; see http://www.emacswiki.org/emacs/TextFormattingRules#toc1