[c-utils] new case study (mostly original code; without Frama-C files)

c-utils/.gitignore

c-utils/CHANGELOG.md

c-utils/LICENSE

c-utils/Makefile

c-utils/README.md

c-utils/examples/bitarray_example.c

c-utils/examples/doublylinkedlist_example.c

c-utils/examples/fileutils_example.c

c-utils/examples/graph_example.c

c-utils/examples/linkedlist_example.c

c-utils/examples/permutations_example.c

c-utils/examples/queue_example.c

c-utils/examples/stack_example.c

c-utils/examples/stringlib_example.c

c-utils/examples/test.c

c-utils/examples/timing_example.c

c-utils/libs/.gitkeep

c-utils/src/bitarray.c

c-utils/src/bitarray.h

c-utils/src/dllist.c