Rectangle constructor is explicit only for 1 parameter.
Rule of zero for Rectangle copy constructor and destructor.
Used list initialization syntax for return.
Merge remote-tracking branch 'upstream/cpp11' into cpp11
Simplified Rectangle construction.
Replaced push functions by emplace functions.
Removed useless const qualifications for integer return types.
Left only two meaningful constructors with two and four parameters.
Merge pull request #580 from Morwenn/cpp11

Revamp Rectangle construction, use emplace functions, clean return types