fixes

1) eraseData doesn't work for me under OSX with iTerm2 or the default term. This seems to fix it (copied from another node ansi module)
2) changing the default value of the current color to 39 seems to make more sense, because `Colorer.reset()` does `_setColorCode( base + 39 )`, not `_setColorCode( null )`. This makes possible to implement something like saveState()/restoreState(), otherwise `_setColorCode( null )` doesn't work.