log undefined and null as empty string (not boolean)
add rountrip test
proper null support and quoted strings
typo and semicolons
moar tests
Merge pull request #5 from csquared/log-undefined-and-null

null and undefined blow up on toString(), so let's nullify them

logfmt.log({foo: null}) will log foo=, which will then get parsed back as {foo: null}

however, logfmt.log(foo: ''} will log to foo="", which will then get parsed back as {foo: ''}

also, added proper support for logging strings with quotes in them.