Advance to C++14

• This simplifies a lot the documentation installation of Ceres.
• The CMakeLists.txt is currently checking for c++11 and c++0x.. I think it is not correct..

added To Do (future) label

changed the description

created merge request !429 (merged) to address this issue

mentioned in merge request !429 (merged)

closed with merge request !429 (merged)

mentioned in commit 3d33f135