EntityManager.get(): Don't create new objects when specified entity/component type does not exist.
Merge pull request #8 from ivarboms/entitymanager-get-fix

EntityManager.get(): Don't create new objects when specified entity/comp...
Add high precision timer.
System::step now takes delta time as a float instead of an unsigned int.
SystemManager.h: Use high precision timer for calculating frame delta times.
Replace NULL with nullptr.
Merge branch 'master' into high-precision-timing