Add annotator support

bob/bio/base/__init__.py

bob/bio/base/annotator/Base.py

bob/bio/base/annotator/Callable.py

bob/bio/base/annotator/FailSafe.py

bob/bio/base/annotator/__init__.py

bob/bio/base/script/annotate.py

bob/bio/base/test/dummy/annotator.py

bob/bio/base/test/test_annotators.py

doc/annotations.rst

doc/extra-intersphinx.txt

doc/implemented.rst

doc/index.rst

doc/py_api.rst

requirements.txt

setup.py