pad: a control nobody planned, in a repository of its own, to prove that
anyone can make one. A square with a dot in it that the pointer drags
around, written outside ../toolkit against its written contract (the
WRITING A PART and THE EVENTS sections of ../toolkit/README) and
nothing else, beside two of the toolkit's standard scroll bars that
move with the dot and move it.

  pad.talc              the program and the control
  examples/drive.talc   what the regress plays at it: hover, a drag far out
                        of the square and the window, the drift home
  examples/*.ppm        the pictures expected at each step
  scripts/build.sh      builds pad.talc into bin/pad
  scripts/regress.sh    runs it under ../screen with no card and compares

Build:

  scripts/build.sh
  scripts/regress.sh

which need the installed toolchain (compiler on PATH), ../canvas built
(its fonts), ../look, ../toolkit, and for the regress ../screen built.
Start it from the launcher (`pad`) or the screen's -run.

WHAT IT USES, one of everything a control of one's own needs:
  the pointer held     from a press on the square until the release every
                       motion comes to it wherever the pointer went: the
                       dot follows out of the square, out of the window,
                       and back
  enter and leave      the dot wears a ring while the pointer is over the square
  times                a second press within 400 ms of the first puts the
                       dot in the middle
  wakes                let go, the dot drifts home a step every 30 ms,
                       each step asking for the next
  a margin             the layout keeps six pixels around the square
  the theme's lines    pad-dot's colour (the accent's when the theme has
                       none), pad-dot's size (from the bevel), the square's
                       ground style (the wells'): a theme that never heard
                       of a pad styles it, and one that cares adds three lines
  standard parts       the bars are the toolkit's, driven by the dot through
                       the same calls any program makes

Nothing here is privileged: the square is made with toolkit-part-create
like the toolkit's own parts, draws with the look's elements, and runs
on the same loop.