documentation improvements

AUTHORS.md

README.rst

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/runner.py

docs/source/_static/logo.png

docs/source/conf.py

docs/source/docs.rst

docs/source/index.rst

docs/source/reference/adaptive.learner.base_learner.rst

docs/source/reference/adaptive.learner.triangulation.rst

docs/source/reference/adaptive.rst

docs/source/reference/adaptive.runner.extras.rst