Adding slope screening code

AUTHORS.md

CONTRIBUTING.md

requirements.txt

setup.py

src/__init__.py

src/__version.py

src/dictionaries.py

src/screening/__init__.py

src/screening/ascreening.py

src/screening/gap_ptest.c

src/screening/gap_ptest.pyx

src/screening/gap_rqtest.c

src/screening/gap_rqtest.pyx

src/screening/kappa_test.c

src/screening/kappa_test.pyx

src/screening/singletest.py

src/screening/utils.c

src/screening/utils.pyx

src/solver/parameters.py

src/solver/prox.py