datapoints(): Avoid bogus "&_=" api parameter and escape user/d

* Passing "cache: true" will make jQuery not
  pass the bogus "&_=123" parameter that is causing a warning.
* Convert to $.ajax syntax since $.getJSON does not have options object for "cache".
* Use "data" options so that "user" and "d" are properly encoded for the url.
Merge pull request #1 from Krinkle/patch-1

datapoints(): Avoid bogus "&_=" api parameter and escape user/d