Support "passthrough" printing

[byteit101]

Sometimes I have pre-colored strings I want to print. It would be nice if notcurses supported parsing and converting those strings so I don't have to.

Today, the first one vanishes, and the second one print out in blue:

ncplane_putstr(n, "\x1b[34ma ═ nccolor\x1b[0m\n");
//...
printf("\x1b[34ma ═ directcolor\x1b[0m\n");