windows: restore cursor location correctly

terminfo: regenerate all entries

Previously we had lost StrikeThrough, and this fixes a few other
discrepancies.  This was generated on Ubuntu Noble (24.04), after
installing the following packages: ncurses-term kitty-terminfo

Try not to clear screen on Windows if TCELL_ALTSCREEN=disable

fixes #621 Unicode disappears if requested twice on the same place on…

… Windows

fixes #606 Want ColorNone to preserve existing color(s)

While here, consolidate the use of the Fill() function from
CellBuffer (eliminating redundant code).

minor style fixup

Fix status badges (broken by shields.io)

minor markup fixes

Better handling for monochrome.

We will automatically select an inverse video mode if we cannot
find any colors at all.  This should help some fallbacks.

Send AttrOff when clearing the screen (#523)

In tcell v2.4, the following calls would reset the screen
to its default color:

1. SetContent() to change the bg color to maroon.
2. Clear()
3. Show()

In tcell v2.5, the behavior changed to clear the screen
to the last-used style passed to SetContent.

This happens because commit 62f5502 set the dirty flag
to false for all cells, on the assumption that sending
ti.Clear would clear the cells anyway. Unlike the drawCell
calls triggered by the dirty flag, however, clearScreen
does not send AttrOff. This causes the screen to clear
to the last-used background color.