Add Core::CollapsedVector

[SimBe195]

Vector that is automatically collapsed down to one element if all entries have the same value
From the outside it behaves like a normal vector. Whether it is collapsed or not only matters internally.

Example:

CollapsedVector<int> v;  // Internal data of v is [] with logical size 0
v.push_back(5);  // Normal push. Internal data of v is [5] with logical size 1
v.push_back(5);  // v stays collapsed. Internal data of v is [5] with logical size 2
std::cout << v.size() << std::endl;  // Prints "2"
std::cout << v[1] << std::endl;  // Prints "5"
v.push_back(6);  // v is expanded because the new value is different. Internal data of v is [5, 5, 6] with logical size 3
std::cout << v[2] << std::endl;  // Prints "6"
v.clear();  // Internal data of v is [] with logical size 0.

[curufinwe]

In addition to inline comments, please also add inline to the function definitions, s.t. the linker does not treat it as an error if two object files with the same symbol are linked together.