This commit also changes the behavior of ProgressContext.IsFinished.
Only tasks that have been started will be taken into consideration,
and not indeterminate tasks.
Closes#329Closes#331
This makes it possible for encoders to output better representation
of the actual objects instead of working with chopped up segments.
* IAnsiConsole.Write now takes an IRenderable instead of segments
* Calculating cell width does no longer require a render context
* Removed RenderContext.LegacyConsole
* Removed RenderContext.Encoding
* Added Capabilities.Unicode
