add support for semicont/semiint variables; make binary a first-class citizen again.
update quadmodel test for Mosek funny business.
update bnatt350 example.
update REQURE.
add upper bound on MPB version.
Update REQUIRE
Update REQUIRE
Merge pull request #244 from JuliaOpt/semicont

[RFC] semi-continuous/semi-integer variables; binary is first-class citizen again