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 moves the rendering logic to draw the grid, to draw strings, and to
draw the cursor into the renderere module. In addition to being an
organizational improvement, this also allowed for some optimizations
managing OpenGL state. Render times for a moderate screen of text
dropped from ~10ms to ~4ms.
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).
Joe Wilm