Implement Bright Foreground Colors.

The `_COLOR_BRIGHT` flag should be separated into `_COLOR_FGBRIGHT` and `_COLOR_BGBRIGHT` to allow accessing the upper 8 colors in ANSI mode. Particularly this allows access to bright and bold colors.

The output coding currently as: https://github.com/GothenburgBitFactory/libshared/blob/ba9b76db8f6180dc62f0bdbdd012891d818108e8/src/Color.cpp#L487 would then be changed to:
```c
result += colorstring[((_value & _COLOR_FGBRIGHT ? 89 : 29) + (_value & _COLOR_FG))];
```

Currently it's possible to trick the existing code into giving bright and bold colors by requesting `inverse bright bold on ` but this is really quite ugly.