The iterator methods simplify logic in the main grid render function. To
disambiguate iterator methods from those returning counts (and to free
up names), the `rows()` and `cols()` methods on `Grid` have been renamed
to `num_rows()` and `num_cols()`, respectively.
This patch introduces basic support for terminal emulation. Basic means
commands that don't use paging and are not full screen applications like
vim or tmux. Some paging applications are working properly, such as as
`git log`. Other pagers work reasonably well as long as the help menu is
not accessed.
There is now a central Rgb color type which is shared by the renderer,
terminal emulation, and the pty parser.
The parser no longer owns a Handler. Instead, a mutable reference to a
Handler is provided whenever advancing the parser. This resolved some
potential ownership issues (eg parser owning the `Term` type would've
been unworkable).
OpenGL only supports shared alpha blending. Subpixel font rendering
requires using the font RGB values as alpha masks for the corresponding
RGB channels. To support this, blending is implemented in the fragment
shader.
The grid holds the state of the terminal with row-major ordering.
Eventually, the grid::Cell type will hold other attributes such as
color, background color, decorations, and weight.
An initialization list is added for common ASCII symbols.
Joe Wilm