Device vector and unordered set functionalities

[kstppd]

This PR adds the following functionalities:

• A Device Vector class in include/splitvector/devicevec.h which is essentially a splitvector using device memory.
• An Unordered Set implementation following the logic of Hahsinator.
  A big rename has taken place where now hashinator.h is renamed and moved to include/hashinator/hashmap/hashmap.h, to accommodate for the new include/hashinator/unordered_set/unordered_set.h

[markusbattarbee]

Having hashmap.h and unordered_set.h in subdirectories completely solo seems a bit daft to me.

[kstppd]

Having hashmap.h and unordered_set.h in subdirectories completely solo seems a bit daft to me.

@markusbattarbee I agree. I pushed again with them one dir up.

[markusbattarbee]

So here's food for thought.
Currently the device vector is a completely separate entity. There is no base class, no class inheritance, and that means that any hash map or set functionality (or splitvector methods such as the new looping reductions) which take splitvector as an input cannot use devicevectors.

Would it make sense to have a basevector class (which also has any shared methods), and have splitvectors and devicevectors inherit that? Then perhaps the methods could build on that class. Or, alternatively, have devicevector inherit splitvector and just override any methods which are not wanted.