ANSI escape sequences like `\x1b[48;5;10m` were not supported until now.
Specifically, the second attribute, 5, says that the following attribute
is a color index.
The ref tests were updated since `enum Color` variants changed.
Ref tests use a recording of the terminal protocol and a serialization
of the grid state to check that the parsing and action handling systems
produce the correct result. Ref tests may be recorded by running
alacritty with `--ref-test` and closing the terminal by using the window
"X" button. At that point, the recording is fully written to disk, and a
serialization of important state is recorded. Those files should be
moved to an appropriate folder in the `tests/ref/` tree, and the
`ref_test!` macro invocation should be updated accordingly.
A couple of changes were necessary to make this work:
* Ref tests shouldn't create a pty; the pty was refactored out of the
`Term` type.
* Repeatable lines/cols were needed; on startup, the terminal is resized
* by default to 80x24 though that may be changed by passing
`--dimensions w h`.
* Calculating window size based on desired rows/columns and font metrics
required making load_font callable multiple times.
* Refactor types into library crate so they may be imported in an
integration test.
* A whole bunch of types needed symmetric serialization and
deserialization. Mostly this was just adding derives, but the custom
deserialization of Rgb had to change to a deserialize_with function.
This initially adds one ref test as a sanity check, and more will be
added in subsequent commits. This initial ref tests just starts the
terminal and runs `ll`.
