Merge branch 'swift-velociraptor-C' into 'master'

.gitignore

configure.ac

examples/EAGLE_25/eagle_25.yml

examples/EAGLE_6/eagle_6.yml

examples/EAGLE_6/testVELOCIraptor.sh

examples/Makefile.am

examples/SmallCosmoVolume/small_cosmo_volume.yml

examples/SmallCosmoVolume/stf_input_6dfof_dmonly_sub.cfg

examples/main.c

src/Makefile.am

src/common_io.h

src/engine.c

src/engine.h

src/swift.h

src/swift_vel_part.h

src/velociraptor_interface.c

src/velociraptor_interface.h