[eacsl] Update copyright year to 2021

...ins/e-acsl/share/e-acsl/libc_replacements/e_acsl_string.h

...acsl/share/e-acsl/numerical_model/e_acsl_floating_point.c

...acsl/share/e-acsl/numerical_model/e_acsl_floating_point.h

...gins/e-acsl/share/e-acsl/numerical_model/e_acsl_gmp_api.h

...e/e-acsl/observation_model/bittree_model/e_acsl_bittree.c

...e/e-acsl/observation_model/bittree_model/e_acsl_bittree.h

...on_model/bittree_model/e_acsl_bittree_observation_model.c

...rvation_model/bittree_model/e_acsl_bittree_omodel_debug.c

..._model/bittree_model/e_acsl_bittree_timestamp_retrieval.c

...ugins/e-acsl/share/e-acsl/observation_model/e_acsl_heap.c

...ugins/e-acsl/share/e-acsl/observation_model/e_acsl_heap.h

...share/e-acsl/observation_model/e_acsl_observation_model.c

...share/e-acsl/observation_model/e_acsl_observation_model.h

...e-acsl/observation_model/internals/e_acsl_heap_tracking.c

...e-acsl/observation_model/internals/e_acsl_heap_tracking.h

.../e-acsl/observation_model/internals/e_acsl_omodel_debug.h

...-acsl/observation_model/internals/e_acsl_safe_locations.c

...-acsl/observation_model/internals/e_acsl_safe_locations.h

.../observation_model/internals/e_acsl_timestamp_retrieval.h

...on_model/segment_model/e_acsl_segment_observation_model.c