Merge pull request #47 from kbansal/sets

Sets theory operators in SMTLIB2 and kinds to use from API have changed. They now are:

SMTLIB: emptyset, singleton*, insert*, union, intersection, setminus, member*, subset*
API: EMPTYSET, SINGLETON*, INSERT*, UNION, INTERSECTION, SETMINUS, MEMBER, SUBSET

(those marked with [*] have changed or been added, others are as earlier)

In the set-logic string use FS to enable sets.

A not-so-well-tested perl command for translating old benchmarks:
  perl -pi -e 's/\(set-logic (.+)_SETS\)/\(set-logic \1FS\)/; s/\(in\b/\(member/g; s/\(setenum\b/\(singleton/g; s/\(subseteq\b/\(subset/g; '

diff --cc src/printer/smt2/smt2_printer.cpp
Simple merge