adhere to PEP008 by using absolute imports

adaptive/__init__.py

adaptive/learner/__init__.py

adaptive/learner/average_learner.py

adaptive/learner/balancing_learner.py

adaptive/learner/base_learner.py

adaptive/learner/data_saver.py

adaptive/learner/integrator_learner.py

adaptive/learner/learner1D.py

adaptive/learner/learner2D.py

adaptive/learner/learnerND.py

adaptive/learner/skopt_learner.py

adaptive/notebook_integration.py

adaptive/runner.py

adaptive/tests/test_average_learner.py

adaptive/tests/test_balancing_learner.py

adaptive/tests/test_cquad.py

adaptive/tests/test_learner1d.py

adaptive/tests/test_learnernd.py

adaptive/tests/test_notebook_integration.py

adaptive/tests/test_runner.py