Add JSON output support

[GZGavinZhao]

Read this on HackerNews and agreed with it. I wanted to make autobuild work with pipes hence the introduction of the -q,--quiet argument, but it was annoying to get it working while avoiding huge if statements and code duplication. Having a --json flag and then process the output through jq may be better both on the developer's side and on user's side (i.e. more control over what information to keep and what to discard).

At least to autobuild query, maybe to autobuild diff as well. I don't think it's that useful for autobuild push?