function __e_acsl_offset now returns size_t (fixed gitlab issue #10)

src/plugins/e-acsl/doc/Changelog

...e-acsl/share/e-acsl/bittree_model/e_acsl_bittree_mmodel.c

src/plugins/e-acsl/share/e-acsl/e_acsl.h

...e-acsl/share/e-acsl/segment_model/e_acsl_segment_mmodel.c

src/plugins/e-acsl/tests/runtime/oracle/gen_offset.c

src/plugins/e-acsl/translate.ml