Jug

* Include requirements files in distribution

* Improvements to webstatus (by Robert Denham)
* Removed Python 2.7 support
* Fix output encoding for Python 3.8
* Fix bug mixing mapreduce() & status --cache
* Make block_access (used in mapreduce()) much faster (20x)
* Fix important redis bug
* More precise output in `cleanup` command

* Fix jug argument parsing

* Fix handling of `JUG_EXIT_IF_FILE_EXISTS` environmental variable
* Fix passing an argument to jug.main() function
* Extend `--pdb` to exceptions raised while importing the jugfile (issue
79)

* jug.backend.base_store has 1 new method 'listlocks'
* jug.backend.base_lock has 2 new methods 'fail' and 'is_failed'
* Add 'jug execute --keep-failed' to preserve locks on failing tasks.
* Add 'jug cleanup --failed-only' to remove locks from failed tasks
* 'jug status' and 'jug graph' now display failed tasks
* Check environmental exit variables by default (suggested by Renato Alves, issue 66)
* Fix 'jug sleep-until' in the presence of barrier() (issue 71)

* Fix saving on newer version of numpy