fix. small one, remove "print"
fix. remove any metric attributes prefixed by '_'
mod. renamed method from "process" to "format" on request parameters.  This is more appropriate since this method should simply ensure that input is properly formed and HTML safe.
mod. use static default datetimes.
fix. paths.
mod. edit rate metric to utilize user map period types to compute range over which rate is measured.
mod. Moved query modules into sub-package user_metrics.query.
add. method UserMetric::_pack_params().  Constructs a list of metric parameter data.
add. method UserMetric::_unpack_params().  unpacks output from UserMetric::_pack_params().
mod. extend build_namedtuple to handle bool types also
mod. parameter "t" is generalized to all metrics.  Add mapping.
mod. namespace of edits now utilizes UserMetricPeriod objects to determine time range of requests.
fix. import dateutil.parser.parse method in place of usage from user_metric module (in general libraries should be improted directly).
add. map_user_id method stub.  This is functionality that will be required to map groups of user IDs between projects.
Merge pull request #7 from rfaulkner/master

Modify metrics to use UserMetricPeriod classes in user_metrics.metrics.users module / tox / user_metrics.query module