Add runner type (#118)

* Add runner_type option

* pre-commit

* Fix max_iters

* Add by_epoch to EvalHook

* Add test_eval_hook for epoch runner

* Remove runner-type arg from tools/train

* Add missing every_n_iters check for epoch mode

* Bump mmcv min version

* Use build_runner

* Use interval in tests

* Update test_eval_hook.py

* Use every_n_epochs instead of every_n_iters. Update DistEvalHook

* Add test_dist_eval_hook_epoch

* Fix tests

* Add DeprecationWarning

* Update docs

* Replace DeprecationWarning with UserWarning