Replace the old pad iso metrics class with a script

bob/pad/base/__init__.py

bob/pad/base/evaluation/PadIsoMetrics.py

bob/pad/base/evaluation/__init__.py

bob/pad/base/script/metrics.py

bob/pad/base/script/pad.py

bob/pad/base/test/test_PadIsoMetrics.py

doc/implementation.rst

doc/implemented.rst

doc/py_api.rst

setup.py

version.txt