[e-acsl] full reimplementation of environment

src/plugins/e-acsl/TODO

src/plugins/e-acsl/env.ml

src/plugins/e-acsl/env.mli

src/plugins/e-acsl/main.ml

src/plugins/e-acsl/mpz.ml

src/plugins/e-acsl/mpz.mli

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

src/plugins/e-acsl/tests/e-acsl-runtime/at.i

src/plugins/e-acsl/tests/e-acsl-runtime/lazy.i

src/plugins/e-acsl/tests/e-acsl-runtime/nested_code_annot.i

...gins/e-acsl/tests/e-acsl-runtime/oracle/addrOf.res.oracle

...ugins/e-acsl/tests/e-acsl-runtime/oracle/arith.res.oracle

...ugins/e-acsl/tests/e-acsl-runtime/oracle/array.res.oracle

src/plugins/e-acsl/tests/e-acsl-runtime/oracle/at.err.oracle

src/plugins/e-acsl/tests/e-acsl-runtime/oracle/at.res.oracle

...lugins/e-acsl/tests/e-acsl-runtime/oracle/cast.res.oracle

.../e-acsl/tests/e-acsl-runtime/oracle/comparison.res.oracle

.../tests/e-acsl-runtime/oracle/function_contract.res.oracle

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

...ugins/e-acsl/tests/e-acsl-runtime/oracle/gen_comparison.c