Provide the timestamps from EVE API calls to callers of EVELink APIs.

THIS BREAKS BACKWARDS COMPATIBILITY.

All EVELink APIs have been modified to an evelink.api.APIResult, which is a namedtuple with 3 fields: result, timestamp, and expires. The second and third fields are the UNIX timestamp values corresponding to the currentTime and cachedUntil fields from the EVE API response that generated the rest of the returned data.

Thus, an API call which used to return a single value (e.g. a dict) now returns a tuple of 3 values - the dict, and two integers. API calls which used to return more than one value now return a tuple of 3 values where the first value is a tuple of the original values. Where possible, accessing the namedtuple fields via their names (e.g. foo.result, foo.timestamp) is preferred over their indices, as it reduces the chances your code will break if new fields are ever added.

Fixes #120.