#89: added '--created now' option

[bvngee]

Changed --created flag to a StringVarP() so that it can optionally be set to now to automatically get the current timestamp, instead of just a manually passing a timestamp.

If the given timestamp is not parseable or "now", it still errors, just from later down the chain instead of by the cobra parser.

Closes #89

(not a go programmer, lmk if you want it done differently)