add json format output

[jcarnu]

This PR intends to add json output to code2pg so that restults can be used in various ways to assess several projects code bases.

Some changes are just reformatting.

I just have some doubts about the ^M sed patch that was automagically transformed by editor and I was wondering it there was a way to fix it with \r rather than ^M ?

https://github.com/societe-generale/code2pg/compare/master...jcarnu:code2pg:json-output?expand=1#diff-46bb443ce3ce993fdf037f881d6a776c920196050f48d503f8ec6c4349f337cbR4367-R4368

Thus, this PR is not ready yet this problem should be taken into account before merging.