Avoid extra quotes where not strictly necessary.

It's not necessary to enclose in quotes every single string value
in log2met format; when using basic words, it's possible to not
quote it (as heroku does for its own logging). This keeps the
logs easier on the human eye.
Make the test more robust
Avoid using regexp
Fix test to adjust for missing quotes
Merge pull request #92 from rasky/no-extra-quoting

Avoid extra quotes where not strictly necessary.