Remove Loki as a dependency, require C++11 support in library
This MR removes Loki as a dependency of Nektar++ and enables the requirement of C++11 for compiling Nektar++. In particular the following changes are made:
Loki::Singletonis removed for our factory holders, instead using a simple
staticvariable inside a static function, which is guaranteed to be thread-safe in C++11.
- CMake configuration is set up to require C++11
- Boost preprocessor headers have been removed in deference to variadic templates in the factory, manager and memory manager.
.clang-formatupdated to C++11