add option for structured output

[lzybkr]

Consider adding a flag to output structured data such as json or csv for use by other tools.

rg --color None --no-heading is nearly good enough, but the extent of the match is missing.

[BurntSushi]

Can you use the --vimgrep flag for this?

It feels a little off to support CSV or JSON in a tool like this to be honest, but I'm not strongly opposed.

[lzybkr]

--vimgrep is roughly CSV but with :, so that works. It's missing the length though.

[BurntSushi]

I'm going to close this in favor of #162. I feel like supporting this would add significant complexity, because every single flag that controls output needs to be re-interpreted based on the output format.

Once #162 is done and there exists a straight-forward path to support this, then I'd be happy to maintain a well tested implementation in ripgrep proper.