Add CodeExporter, fixes #30

[geek-merlin]

For usage see readme stub in code.

[geek-merlin]

Memo: https://github.com/geeks4change/varexporter/tree/code-exporter-on-040

    "extra": {
        "patches": {
            "brick/varexporter": {
                "Allow literal code https://github.com/brick/varexporter/pull/32": "https://github.com/geeks4change/varexporter/commit/999cd7f918e2445460f41bed054e96d2b2d1c5dd.diff"
            }
        }
    }

[geek-merlin]

Hmm, seems like i messed sth up, the MR show 91 commits, in fact it is 1:
geeks4change/varexporter@677b5cd...999cd7f

[geek-merlin]

NOW we've got a clean MR. Sorry for the noise.

[geek-merlin]

MEMO: A composer install needs a different patch as it has no readme (why?): https://github.com/brick/varexporter/commit/ae1a606cd8c462b7ec89511e202296ceb4a5c254.patch