Apply proper changes for pairs to be used as a package

LICENSE

examples/kernels

examples/kernels.pdf

examples/lift.py

examples/lj_embedded.py

examples/lj_func.py

examples/lj_ns.cpp

pyproject.toml

setup.py

src/__init__.py

src/pairs/__init__.py

src/pairs/code_gen/__init__.py

src/pairs/code_gen/cgen.py

src/pairs/code_gen/printer.py

src/pairs/coupling/__init__.py

src/pairs/coupling/parse_cpp.py

src/pairs/graph/__init__.py

src/pairs/graph/graphviz.py

src/pairs/ir/__init__.py

src/pairs/ir/arrays.py