Introduced enum "Polarity" for POS, NEG.
The literals-field of clause_info only needs to contain the literal-array.

And using "new".
Using std::realloc (this usage is kind of okay, at least for now).
Renaming: "variables" are mostly "literals".

And
 "var_in_clauses" -> "clause_occ"
 "var_in_clause_locs" -> "clause_index".
Timing update.