Black background text options

[ars-ka0s]

I'm sensitive to high-contrast text especially white background, so added two color modes with black backgrounds. Figured other people may want similar options.

-t 5 uses the default background color and basic 8-color commands, which should let most terminal emulators apply their own color theme.
-t 6 uses the RGB commands like the 1.6 default -t 1 which gives a stark black background.

For the Windows side, -t 2 does a dark background mode.

As always, glad to tweak if preferred to be implemented differently.

[ars-ka0s]

Rebased to current dev

[ars-ka0s]

Rebased to current dev.

Does seem like this would fix #477 but no feedback yet from people mentioning they'd test.

[sarcasticadmin]

These new options work for me on linux:

Heres some info about my terminal as well if it helps:

$ echo $TERM
screen-256color
$ echo $XTERM_VERSION
XTerm(384)

[opswhisperer]

Would love to see this get merged

[sarcasticadmin]

Is there anything left to do? @ars-ka0s @wb2osz