add a config settings and flag for colours

Colours can be enabled in two ways:

- Add Color to pacman.conf. This enables colours automatically.
- Use --color=WHEN where WHEN is none/auto/always.

WHEN as 'never' disables colours (overrides config file), as 'auto'
enables colours when stdout is a tty, and 'always' enables colours no
matter what.

Signed-off-by: Simon Gomizelj <simongmzlj@gmail.com>
introduce colstr for colourizing

colstr_t colstr will hold the colourizing agents.

Signed-off-by: Simon Gomizelj <simongmzlj@gmail.com>
colourize colon_printf and question

Signed-off-by: Simon Gomizelj <simongmzlj@gmail.com>
colourize warnings and errors

Signed-off-by: Simon Gomizelj <simongmzlj@gmail.com>
colourize table output

Signed-off-by: Simon Gomizelj <simongmzlj@gmail.com>
colourize the output if -Qi/Si

Signed-off-by: Simon Gomizelj <simongmzlj@gmail.com>
colourize -Ss/-Qs
colourize -Sl/-Ql

Signed-off-by: Simon Gomizelj <simongmzlj@gmail.com>
colourize -Q

Signed-off-by: Simon Gomizelj <simongmzlj@gmail.com>
update documentation and config files

Signed-off-by: Simon Gomizelj <simongmzlj@gmail.com>