respect escaped quotes in the valueRxString regex

[beniwohli]

This resolves #2. The regex proposed in https://github.com/logstash-plugins/logstash-filter-kv/issues/2#issuecomment-137837605 turned out to not work correctly, and it was extremely slow (the test suite never finished). Instead, I adapted the regex from http://stackoverflow.com/a/10786066/45691. Here's the regex on regexdoc: https://regex101.com/r/wN6qS3/1.

[elasticsearch-release]

Jenkins standing by to test this. If you aren't a maintainer, you can ignore this comment. Someone with commit access, please review this and clear it for Jenkins to run; then say 'jenkins, test it'.

[beniwohli]

Is there any interest in this PR? I'll gladly spend the time to fix the merge conflicts that have accrued since opening it, but only if there's interest in merging it.

[jordansissel]

Howdy! Sorry for the delays.

I like the idea as proposed. I have a question about the behavior, though. It feels like the escaped characters should be interpreted before storing in the event. For example, for a kv input of this:

foo="hello \"world\""

The resulting value for the foo field should be hello "world" (no backslashes). The way I read your tests, it seems like the backslashes are kept. Thoughts?

[beniwohli]

Thanks for the feedback. Yes, you're right, the quoting back slashes shouldn't end up in the resulting string. I'll see if I can tweak the regex (it's been a while since I fully understood that regex, though :D )