add support for created and expires values

[blacktemplar]

Resolves #109.

Adds support for created and expires values in parser and signer.

[zetxx]

+1 is anyone on this ?

[jasonbking]

I'll try to get this reviewed sometime the next several days..

[jasonbking]

Aside from the one question, please run 'make check' -- there's a number of small lint + style errors it is flagging (that's the Jenkins failure). That will need to be clean before it can be merged.

Also, would you be willing to add a couple of tests since you're adding more logic to the parsing? I think a test that correctly parses a number parameter, as well as one that correctly catches an incorrectly formatted number (e.g. param=123foo456 or such) would be fine.

[blacktemplar]

I fixed all make check errors and added some new tests, testing the parsing behavior.

make test runs through except for one test (not ok 10 test/examples.test.js) which I think is unrelated to my pull request and also fails on my machine on the master branch.

But the CI still fails, so I am not sure whats the fault.

PS: would be good to document somewhere that one needs to install the npm package json globally to use make check, at least I didn't find it anywhere and needed some googling.