Build without TCL_WIKI.
Provide a function `rawhandler()`, so that user-defined spans of input can be passed through without modification.
- Add option `-r` to control `rawhandler()` function, and `-a` for ASCIIMath.

Use the `rawhandler()` function to implement support for ASCIIMath (http://www1.chapman.edu/~jipsen/mathml/asciimath.html) via option `-a`.

*NOTE:* This targets a modified version of `ASCIIMathML.js`, where U+0060 (the *Markdown* backtick) is replaced with U+F8F0 (from the Unicode PUA).
*NOTE:* The `-a` option does *also* prepare for `$` and `$$` to delimit LaTeX-like notation (inline rsp display style).
*NOTE:* While `-a` does accept `\u00AB` Unicode escapes (but only up to `\u00FF` !), the `-r` option does not (yet).