New CSBI method. atexit fix, better list_tags().

Previous GetConsoleScreenBufferInfo code worked everywhere except in
Python 2.7 x64. Trying a new way for 100% compatibility.

Improved list_tags() sorting.

_reset_colors() sets absolute colors instead of going through
_set_color(). Since the black background code is 0, which also indicates
the user is only setting the foreground color, _reset_colors() should
set the already-known fg and bg colors itself. Before it was not
resetting the background color.