Choose to clear background for TTY

[MitchNine]

I want to be able to have a background colour for the output in tty. This would help in getting a nicer looking code snippet in projects like https://charm.sh/.

The functionality of clearing the background is still present. But now it is done explicitly though the style.ClearBackgound() function. An example of this would look like the following:

func main() {
	in := `int main(int argc, char** argv) { return 0; }`

	lexer := lexers.Get("C")
	if lexer == nil {
		lexer = lexers.Fallback
	}
	style := styles.Get("monokai")
	if style == nil {
		style = styles.Fallback
	}
	formatter := formatters.Get("terminal256BG") // Formats with the BG suffix in the name have background colours enabled
	if formatter == nil {
		formatter = formatters.Fallback
	}

	iterator, _ := lexer.Tokenise(nil, string(in))
	formatter.Format(os.Stdout, style, iterator)
}

[alecthomas]

I don't mind the ability to configure this behaviour, but this is a backwards incompatible behavioural change. It'll have to be opt-out, not opt-in.

[MitchNine]

I don't mind the ability to configure this behaviour, but this is a backwards incompatible behavioural change. It'll have to be opt-out, not opt-in.

Fair enough, I'll see what I can do

[MitchNine]

@alecthomas I've changed the default behavior back to no background colour for tty by default. Couldn't figure out a neat way to specify if we should enable the background colour so instead I've just created formats with the BG suffix that have background colours enabled.