Count allocated bytes

[alphaville]

Main Changes

The total allocated bytes are counted by the instance of the session. Just do

size_t bytes = Session::getInstance().totalAllocatedBytes();

Note, however, that invocations to cudaFree don't have an effect on byte counting. (fixed)

The main changes are:

1. Introduced Session::cudaAllocate(void** d, size_t s)
2. Introduced Session::totalAllocatedBytes()
3. Replaced all cudaMalloc with Session::cudaAllocate
4. Unit test

[ruairimoran]

lgtm. Version bump?

[alphaville]

lgtm. Version bump?

Ah, yes! I'll update it now.