1. Add new pseudo-protocols to `linkylinky()`
* raw: the link is a raw character stream that's dumped to the
output unchanged.
* class: the link is the name of a style, and goes into the
output as `<span class="`_link_`">`_tag_`</span>`. (Used
on pell for [Postoffice](class:caps))
* id: the link is the name of an id, and goes into the output
as `<a id="`_link_`">`_tag_`</a>`.
2. markdown output is now in xhtml.
3. fix an indentation bug with list items (messed up quoting)
4. Add `theme` to the sample programs pile.
5. The version[] string now contains all of the options, not
just the version#
6. remove `MKD_TABSTOP` environment variable, roll it into `MARKDOWN_FLAGS`
7. `pull()` was zeroing the input stream at EOF, thus breaking `linkylinky()`
when a partial tag was at EOF.
8. A bit more chainsaw work.