Updated README with note to install requirements via make
Support validation of enrollment.

* Synthesize validation events from Sqoop dumps of
  student_courseenrollment.

* Compare validation events with enroll/unenroll events.
  Includes unit tests.

* Define "generate-before" option.  When true, generate events from before the defined interval.  Default is false.

* Give Synthetic events timestamps that are a microsecond different from the source events.

* Add CourseEnrollmentValidationPerDateTask to group synthetic events by date.
Add support for multiple "src" arguments for PathSetTask.

Used by answer distribution, course enrollment, user location,
and enrollment reports.
Output user_id in validation event as an int.  Add CreateAllEnrollmentValidationEventsTask.
Include dump start and end time in each validation event.
Reset validation event timestamps if they should be earlier in the dump.
Clean up synthetic event fields.
Add WarehouseMixin to CreateAllEnrollmentValidationEventsTask.
Permit synthesized enrollment events without mode to be processed.
Add placeholders for enrollment mode processing.

The short-term goal is to get mode values output in synthetic events.

Longer term goal is to prepare to handle mode-change events.
Refactor to handle enroll mode.
Pass all arguments from CourseEnrollmentValidationPerDateTask to CourseEnrollmentValidationTask.
Remove mode changes from start state.

Also use current mode when creating events before first real event.
Add MISSING event for course-users with no validation events.
Merge pull request #34 from edx/clintonb/update-mysql-connector-python

Updated README with note to install requirements via make
Merge pull request #31 from edx/brian/validate-enroll

Support validation of enrollment.
Support running the pipeline in a docker container