[Eva] Documents more builtins in the user manual.

Added to the user manual:
- float builtins acos, asin, atan
- wide-character string builtins wmemchr, wcschr, wcslen
- memory builtins memcpy, memset, memmove
- Frama_C_is_base_aligned and Frama_C_offset.

Removes a latex command to distinguish open-source and proprietary features,
as Eva is now entirely open-source.