Follows removed AST nodes in kernel

See merge request frama-c/meta!57

[typing] Improve error message

See merge request frama-c/meta!56

[Tests] test command are executed from result directories

See merge request frama-c/meta!52

Warning instead of abort for unknown functions in target set

See merge request frama-c/meta!54

warning has a category unknown-func, whose status is abort by default.

add \func metavar to denote current function

See merge request frama-c/meta!55

Compile MetAcsl with OCaml 4.13

See merge request frama-c/meta!53

remove Meta_options.StringSet in favor of Meta_utils.StrSet

[kernel-compat] removed AST nodes

See merge request frama-c/meta!51

A lot of code was dedicated to the -meta-eacsl option, meant to
circumvent some limitations of E-ACSL by translating \let and some
\separated forms to equivalent formulas.

E-ACSL no longer has these limitations.