Introducing Master of Ceremonies, a package for presentations

[Psionic K <psionik@positron.solutions>]

I use this package for making videos and presentations.  It's almost
ready for archives.

https://github.com/positron-solutions/master-of-ceremonies
https://github.com/positron-solutions/master-of-ceremonies.git

`mc-focus' is one of the most useful commands.  Select a region, call
it, and that region will be displayed full screen with appropriate
scaling.  You can highlight multiple regions by selecting and using
the "l" key.  The "." key will activate a "subtle" cursor that goes
away after a short number of blinks to assist highlighting without
needing to hide the cursor all the time.  There is a magit-style
interface for learning the rest of the modal bindings, available under
"h".

The `mc-kill-ring-save` command will save an expression that can play
back this display, making it rather easy to step through sequences of
highlights.  This produces high quality illustrations of code that
line up well with explanation.  When combined with dslide (on non-GNU
ELPA and MELPA), the two packages can create effective presentations
about code that are missing almost nothing from dedicated presentation
software.

Many of the tools for accomplishing this were valuable as standalone
modes for presentation
- `mc-quiet-mode' suppresses messages
- `mc-subtle-cursor-mode' is great for using the cursor like a
transient laser pointer
- `mc-face-remap' will remap many faces from presets.  I use this to
tweak faces for  MC Focus screenshots.
- `mc-fixed-frame' sets to preset resolutions for recording videos and
corrects the size when minor actions like resizing buffer text change
the size of the frame

Bindings for built-in Emacs behaviors like hiding the mode line are
provided.  I only need to add support for modifying the transient to
allow myself to add keycast toggling.

These tools have been combined into a one-stop interface, `mc-dispatch'.

The core code for `mc-focus' acquired numerous behaviors I was using
personally and so the code is rather off.  It needs to be
re-architectured for smoothly supporting rectangle selection,
whitespace trimming, and playback.  I have experimented with
translating overlays from the source into the text properties of the
display.

Numerous things work in numerous settings, so I have made it available
ahead of publishing on package archives.  Emacs conf participants may
find it of use for some last minute embellishment.

PRs and issues will be attended to.