libansi: correctly reset attributes

libansi: correctly reset attributes

When resetting the attributes, we were updating last_attr to the unknown value
0x300, which doesn't always work.

For instance, when requesting reset and normal attributes, i.e.
"\e[0;30;47m" with the previous attribute being "\e[1;30;47m", we where printing
"\e[0;47m", which behaves like "\e[0;39;47m". This is incorrect.

This patch adds a flag to explicitly set background and foreground colors after
a reset.

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>