Our tcell library incorrectly referenced tcell color values rather than
just names. The values aren't part of the public API and did change with
the update to v2.
This commit switches our tcell library to using the public constants
exported by the `tcell` project.
Also aligning our color definition of the first 16 colors with `tcell`
and Xterm. Adding two additional colors to make this change backward
compatible with `termbox-go`.
- Documenting color modes.
- Providing helper functions to set colors in different formats.
- Allowing users to set other than the 8 system colors.
Fixes#66
- don't allow partial overwrite of a full-width rune.
- don't allow placement of a full-width rune if it doesn't fit.
- allow callers to also read from the canvas (read-only).
Done here:
- adding helper library which determines area from size and vice versa.
- fixing an off-by-one bug related to area sizes.
- allowing overwrite of cell options by passing an existing cell.Options
instance.
- implementing canvas and its tests.
