dslide 0.4.0, last unstable release

[Psionic K]

Dslide (Domain Specific sLIDEs) is a rethought, mostly complete
rewrite of org-tree-slide.

Its highlight features:
- using babel blocks
- per-slide configuration
- extensible via custom actions and support for custom EIEIO classes

There is a file in the /test directory called demo.org.  You can see
the presentation with `dslide-deck-start' or `dslide-deck-develop' to
watch progress updates be highlighted.

You need my other package, `master-of-ceremonies' to complete the last
slides of the presentation.
https://github.com/positron-solutions/master-of-ceremonies

There are a few areas I plan to change where feedback could be
beneficial.  Stop me if any of these choices seem unintuitive.

I plan to get rid of the idea of independent `DSLIDE_SLIDE_ACTION' and
`DSLIDE_SLIDE_CHILD_ACTION' and instead combine the child and slide
behaviors into several distinct slide classes.  The user will set
`DSLIDE_CLASS` to achieve the combination of these two options.  They
will still accept plist style arguments for small behavior tweaks.

Per-slide actions will still be supported, via `DSLIDE_EXTRA_ACTIONS'
or `DSLIDE_ACTIONS' to completely override the normal actions set via
customize or document properties.

A user asked me to enable hiding babel blocks via setting the
`:exports none`.  I'm not sure if this is consistent with other uses
of that option.
My other option was to re-use the babel block keywords that are
usually already present, adding just "hide" to the normal list of
method names.  You can reply directly if you like:
https://github.com/positron-solutions/dslide/issues/1