* feat(canvas): implement half block marker
A useful technique for the terminal is to use half blocks to draw a grid
of "pixels" on the screen. Because we can set two colors per cell, and
because terminal cells are about twice as tall as they are wide, we can
draw a grid of half blocks that looks like a grid of square pixels.
This commit adds a new `HalfBlock` marker that can be used in the Canvas
widget and the associated HalfBlockGrid.
Also updated demo2 to use the new marker as it looks much nicer.
Adds docs for many of the methods and structs on canvas.
Changes the grid resolution method to return the pixel count
rather than the index of the last pixel.
This is an internal detail with no user impact.
This commit adds a readme to the examples directory with gifs of each
example. This should make it easier to see what each example does
without having to run it.
I modified the examples to fit better in the gifs. Mostly this was just
removing the margins, but for the block example I cleaned up the code a
bit to make it more readable and changed it so the background bug is not
triggered.
For the table example, the combination of Min, Length, and Percent
constraints was causing the table to panic when the terminal was too
small. I changed the example to use the Max constraint instead of the
Length constraint.
The layout example now shows information about how the layout is
constrained on each block (which is now a paragraph with a block).
